These same topics come up every time another comic book character movie comes out. I'll cover my own personal feelings briefly-- I'm not into comic book movies (or comic books) at all. I'm a geek/nerd/gamer/whatever, but never got into that part of the culture. That being said, the Avengers movies, Guardians of the Galaxy, and even the Iron Man movies are all pretty damn good. (Anyone blaming the writer's union for movies being bad is an idiot. Learn how movies are made first, then try to mouth off. I'm a WGA union writer. You don't have the first clue as to what you're talking about.)
So when you're wondering why they keep remaking comic books into movies, or why there is sequel after sequel for these same comic book stories, it is because they (usually) perform well. The studio FOX doesn't usually do many comic book movies-- Kingsman (which performed well) and the X-Men franchise (which does really well also). But both of those pale in comparison to the other comic book movie franchises. One might say that FOX is well out of their element here.
I agree with Speak above-- "Many americans are too stupid to appreciate less action and more complex stories, so it's a race to the bottom. Plus, Now so many tickets are sold overseas, that media companies want movies that you can follow without being an english speaker." Yes, I agree-- especially as it concerns the big summer "tent-pole" movies.
But for those of you who feel that there are no good movies being made, I'd love to make some suggestions. 2015, so far, has been a little bit on the disappointing side for me (and I fricking love movies). For big budget action movies, Avengers2 was good, and Mad Max blew me away with it's story telling *through* action. Spy was good for a comedy. But there have also been some good smaller movies this year-- Ex Machina, Mr Holmes.
Behind on your movies from 2014? Got kids? Be sure to check out Guardians of the Galaxy, LEGO movie, Big Hero 6 (even check them out if you DON'T have kids!). Great movies. Like good action, suspense, drama? Gone Girl, Birdman, Nightcrawler, Edge of Tomorrow, Interstellar, Boyhood. Some great writing. (My almost-teen daughter loves the Hunger Games, Insurgent, Pitch Perfect, Fault in our Stars, etc.)
If you don't like the big action movies of the summer, dig around for indie films, check out local revival theaters (the Paramount here in Austin often does a Summer Classics... see Vertigo and Rear Window back to back on the big screen, or all 3 Godfathers on a long Sunday, etc). Search around. Before you lament (or, in the case of some of you, celebrate) the death of the art of cinema, look around a little. There are some great movies being made today.