Cause it's a great toy which gives persons a reason to unfold their creativity.
I haven't bought a LEGO set now on a very long time, mostly I buy cause of the awesome mini-figs, not about the set itself. However, the bricks and everything else is often if not always of very high quality.
Light-Up lightsabers is a very stupid idea. It makes a mini-fig less poseable and is there just for making children buy the expensive set it comes in. Same with flashlights and all that. Another thing is all the color changes, the "Flesh-Toned" mini-figs looks plain awful and the thrown away original LEGO colors like brown, blue and grey are lost to new disgusting colors.
Buying up Movie Line licenses.
More movie lines, of all these super-hero movies coming I hate that LEGO has decided that there won't be any Spiderman 3 sets.
Remove the mini-figs from the sets and sell them in own boxes for about 5 bucks.
All sets are very expensive, a set like Final Duel II, includes thirteen pieces and two mini-figs. The prize for this is 10-12 bucks while it's worth 5-7 bucks.
That LEGO starts selling their figs in packs.
LEGO will probably already be the best construction toy while rivals like Megablocks will probably be destroyed later. But if not I still say that they shall buy up more Movie Lines cause that will do collectors more eager to buy it just to have a collection. Just look at the masses of Star Wars.