I too would like to see see some demographics by an anthropologist. I have absolutely no idea of the background of this (or really any) franchise's core demographic, but to compare it to my own community: Those were the movies that everyone wanted to see, but nobody really "had the chance." For me, it was because I went to college and am no longer walking distance from a movie theater. All my friends are in a similar situation. While we would probably enjoy the movie the most, theaters IN GENERAL are outdated and inconvenient to people like me. Let me give you an example: Last Saturday, a group of friends and I were bored 3:00 in the morning. "we should watch a movie" one said. Now, do you think it even crossed our minds to find someone to drive us to the movie theater? Of course not. We cycled through Netflix, HBO GO, and ultimately decided to just play Mario Party. Why in the world would we spend $20-$40 for 2 hours when we have everything we could ask for here?
I still plan on watching these movies eventually, but there's a very good chance that when I do, they will have agreed that the movie was a failure and never make another. And I bet I would WANT another movie, but the lag time between money spent and money received is so long that movie makers would have a better return rate buying lottery tickets.
It's always been like this to a degree, producers know this and have been making all the blockbusters in the summer and winter, as that's when most people are on vacation and have the most free time. The problem is that companies have propagated social stigmas in all the places that now would be beneficial. Straight-to-tv/dvd, decreasing theater time, and word-of-mouth promotion has always been seen as an instant flop, but obviously TV shows like Breaking Bad, Walking Dead, and countless others are getting the love of just about everyone in their demographic. And I believe the majority for that is ease of access. Ask anyone on campus how they liked the last episode of Breaking Bad, and they will likely have an opinion. Ask them about any movie released after The Avengers, and you won't be so lucky.