I normally stay out of the squabble and speculation, not my thing but since someone wanted my extra 2 cents on the current debate....
Upon edit & re-read, TLDR seems necessary: TLG is in this theme for the long haul & Diagon Alley seems to have good enough content meriting Gringotts separately down the line.
There are a whole variety of decisions (pros/cons) to weigh out when running any business or launching product. None of them are great secrets either. Sun Tzu's Art of War are more reminders than teaching new ideas of how to run your army/business. Business isn't some super secret code. Look at all your pieces, determine next move, weigh out side affects of your actions, biggest bang for buck etc. MOST business, and I would include TLG in this greatly, more so than almost any other company I've watched, really put their heart and a great deal of thought into their products. Designers, engineers, producers etc themselves LOVE their product and want their customers to enjoy it as well. When I make something that I'm proud of, i want the world to know it, immediately. I would assume that TLG follows the same core internal pride in their product. So... if Gringotts (one of the most iconic buildings in Diagon Alley that would look so beautiful when made with an awesome dragon etc...) isn't currently included in a set called Diagon Alley most of us react the same? "huh? why?" Few things to remember here though. Think of this as a business decision, not from the fan site who wants everything... now.... but then you realize you dont want everything now because you actually can't afford everything now...
1. TLG has clearly seen the resurgence into one of the most popular current pop culture trends of the last 20 years. I honestly believe in 15-20 years Harry Potter, if handled correctly, will surpass Star Wars, (yes, opinion, not fact) in popularity for a few reasons:
Those of us who grew up as kids/teenagers reading and going to the midnight releases of the movies now have kids and income.
Little girls LOVE harry potter. There is no denying that. More on this later down.
The number one demanded set during the 7 year absence of Harry Potter sets was (it is tracked internally in TLG) Harry Potter.
2. With expectations being exceeded the first year, Harry Potter is here to stay for at least the near future. Everything on the walls says so... unless COVID screws us all and everything changes. But as long as status norm is kept, the brand is NOT going away and they are selling like crazy. An normal lineup stays on the shelves for 12-18 months. Hogwarts original launch line is still available from Shop@Home. For a licensed lineup, that is unheard of. Its selling, so it stays. Most iconic location for all of Harry Potter is Hogwarts. The first installations of Great Hall & Whomping Willow sold well enough to earn additional waves. Second most popular/iconic location is Diagon Alley. Even in D2C we've seen a second additional iteration be warranted when first one proved itself.
3. The license itself. This license is for "The Wizarding World" NOT Harry Potter alone (Magical Beasts and other expansions are included, thats not the debate here though on the quality the expanded universe I.P. but the fact that they exist says something). Granted the "branding" has shifted back to Harry Potter but that is not what the license is from. Because another toy company has the license to Harry Potter, I believe (not 100% sure here but I believe it still is though I don't know who, could be directly to Universal themselves and they're now redistributing back out), LEGO got the license for the Wizarding World aka From universal studios from the Parks themselves. With that being the case, when you enter Universal's park area for "Wizarding World"... BAM, there is Gringotts. Its not hidden, its not off to the side, front and center. In case that isn't clear, its important to the park and Wizarding World. This is why the sets are running visually closer to the movies and the park. The park is based on the movies, so the sets are based on the movies. The books aren't being ignored and Easter eggs are there, but... anytime we get a character NOT from the movie should be seen as a bonus and only a bonus, don't come to expect it. Set verbiage from descriptions frequently refer to the movies, NOT the books.
4. LEGO has invested so much into neutralizing the gender gap in their toys. Original Friends franchise said TLG invested 4 years of research (secretive, not public allowed AT ALL) into building out the friends line (lead designer was hired to do just research and study why girls didn't "consume" (buy, enjoy, play with, whatever) LEGO products as much as boys). 4 years of just research, then additional time for the actual sets. LEGO hit a cap of its growth, and the easiest way for them to grow was to go after additional consumers: girls. 200% growth if they could do it correctly because boys were already complete in terms of marketing, interest, how a boy "plays".
TLDR of that 4 year research: Boys play to build, girls build to play which means the enjoyment of the majority of boys is the building process itself. coming up with the idea, executing, and then doing it all over again. Girls tend to prefer keeping the build around for longer and then role-playing more. Girls will also (not always, but frequently) get more upset if you wreck their build because "now i can't play with it" approach.
So if the assumptions are being made correctly and connected...
a brand that will only get more and more popular over time
sells to the demographic that LEGO wants to continue to capture and grow into (point 4 about girls... I don't think I can over state how important growing the girls market has been to LEGO that people constantly forget and overlook)
is here to stay for more than 1,2,3, waves... (might not be 20+ year like star wars, never know, but its def not going away this year or next year). Most people view shinny things on "time" and don't look at the scope of how much product can actually be pushed too. There is a limit to spending habits of consumers. Even collectors have their bounds.
the brand actually doing the license (Universal Studio's Wizarding World) is involved in the process and has visions in mind of their brand and direction. LEGO designers are not on 100% free build for a licensed set. It will have to go through multiple iterations checking in with both companies.
If everything planned in design doesn't fit into scope, you have two choices. Make it fit (at the cost of overall quality potentially) or murder your darlings and make the necessary cuts to content. I would wager that one of the presented builds created at some point included the bank.
Now separately, marketing: How many times have people seen an album released by a band and then the first single out of the gate is NOT the best song. it will be the 2nd or 3rd single pushed from a marketing standpoint to maintain longevity of the album. Take Linkin Park's very first album "Hybrid Theory". For example: "One Step Closer" was their first single (decent song), but even the band commented it was not the best song on the album. Next was "Crawling", Third and final single: their smash hit "In the End" rose the album to new heights. To maintain longevity they opted for this marketing approach. Yes, this can backfire. What happens if people don't initially buy and you put all your money into the first single (not the best one). Quality products will hold up though and its worth it long term. TLG Harry Potter Line has a passion and care that I haven't seen in very many other themes over the last 15 years I've been collecting as an adult. It would appear its holding its old with sales/consumers.
Attention to detail with the figures overall has been 2nd to none and the sets have been well above average. I have absolutely loved both the figures & sets and am grateful they spread things out. I find it easier to purchase 300-400 here, rather than 700-800 up front. I trust the company to do their best by them and am grateful to be able to purchase the sets from a financial standpoint (especially in today's world). Doesn't mean TLG is perfect (I REALLY want more of the other houses) and there aren't other alternatives to all actions, but overall, they've done a pretty good job so far. They can't of done too bad if we're all here chatting about it, right? More than likely, if things go according to an internal plan, I would expect an separate compatible in size and style for Grintgotts at some point. But, the future is always uncertain and shifting. Speculation is just speculation, just ask anyone their expected 2020 plans vs reality.
Now back to lurking....