God's Beard said:
Because it's an obvious marketing gimmick. They're doubling down on the hardcore reader and pushing fan service so hard it's almost unreadable. Because everything is in the same universe, they can push aside and bring back characters and storylines like it's the fucking stock market. Rather than focus on creativity and good art, they have this self-fellating obsession with reworking the same dried out piece of clay until it turns into sand, then they boil the sand into glass and break it. It's more like looney tunes than anything, just character-driven Mad Libs, professional fanfiction to generate hype for figurines and ticket sales.
While somewhat true (especially from a non creator-centric view), it's also a highly cynical view of the entire matter. Discworld - not entirely applicable because it all comes from the mind of one man, but - Discworld is far more enjoyable because everything on the Disc interrelates. Ankh-Morpork in one book is the same Ankh-Morpork in the other book, only something else is happening then. Spiderman's New York is the same as the Fantastic Four's New York, only they're focusing on different things.
And there's other things. Some characters are archetypes, or authors can build off them and use your pre-knowledge of who they are - who they've
been - to create works of complexity, subversion, you name it. Check out Neil Gaiman's
1604, for instance, which requires at least a passing knowledge of the characters of Doctor Doom, Captain America, Daredevil, and so on. Miller's
Dark Knight Returns relies heavily on the Batman before DKR being entirely different to who he is now.
Good art and storytelling shines through no matter whether they take place in a shared universe or not. Judging based on that quantifier alone seems silly to me.