It's a movie, bro. We aren't really there to learn advanced literary techniques, we're there to see shit blow up and some funny lines delivered. If I wanted to consider the problems of the universe, I'd read Shakespeare or Hemmingway or some shit.
You've pretty much summed up the problem with the movie (and entertainment) industry: people are either too ignorant or indifferent about the media they consume being dumbed down to a ridiculous degree. I can't even blame the industry; after all, if you can make billions feeding people the same template, why bother changing? It's not that these movies need to be cinematic masterpieces in the slightest; I can buy into the idea of mindless entertainment to a slight extent. But having at least some
thought-provoking moments or some
unpredictability every now and then would do wonders to those movies. But I guess the payoff is too worthless to even implement those.
The Avengers franchise in particular has also had the added negative effect of moving the industry toward franchises (the most aggravating being the upcoming Avatar franchise when the first movie was one of the worst things I've ever seen). And with the way people are eating up Marvel movies, it won't be long before other franchises are cloning their efforts. DC is already trying to copy Marvel, they just need to add some more red herrings to their movies and they can probably achieve some success (provided they stop shooting themselves in the foot).
I'm not saying you have to like them, just understand why lots of people do.
I legitimately can't understand why people like these movies apart from their kitsch value. I think those movies disrespect their audience by refusing to change up their narrative in the slightest, which is why I can't understand the target audience. Do they want to have some comfort in knowing with complete certainty how the next two-and-a-half hours are going to play out? Or are the various "new" settings and concepts enough to make them believe they're watching an entirely new movie? I honestly want to know what makes these movies so engaging to some (most) people.