The "fiduciary responsibility" answer is that TLG is a company, and should do whatever will make the most money.
Now I often think that's a too-convenient corporate cop-out. And TLG seems to want to "do the right thing" as far as companies go (but then that is also part of their brand positioning, so it's hard to separate from the profit-motive).
My one-person perspective is that the big struggle for LEGO was always to broaden their appeal to girls. Maybe I'm wrong, but I think it was mostly a boy-toy for most of its history. Not completely of course, and I think not with great intentionality, but boys just seemed to be the predominant market for them, whether it was City or Technic or even just building blocks. They tried a few girl-oriented initiatives from time to time, and as far as I know they failed pretty badly. Friends, et. al., appears a much better effort, in part because not "dumbed-down," and therefore much more successful to moving girls into the LEGO market. So is all this LEGO's fault, or a "fault" of the kids for wanting the wrong things?
In an ideal world I think you are right, we should not have these great gender divisions in toys, roles, and so much else in life. I suspect most of what we often think of as innate difference is socialized. But there's a lot of historical weight behind those social norms (as well as probably a pinch of physically-rooted difference), so they evolve only slowly. All of us will have to grind away together for a long time to get to a point of true egalitarianism--so while I guess LEGO should get their slice of that collective responsibility, it seems a bit unfair and probably futile to expect too much of them alone.
For the most part I think they are just providing what their customers want. I agree that there is more TLG could do around the edges to have a few more girl figures in the boy sets, etc. But I suspect the ugly truth is that NexoKnights + Elves just sells a lot better than NexoElves would.