I started reading superhero comics over the last couple of years. I'm enough of a geek that they had appeal, and I also actually didn't know very much about the Marvel/DC universes other than the basic headlines, so I was a bit curious. Also, at the end of the day of being jacked into the intertubes, my brain isn't always up for anything too difficult.
But I got bored after awhile, in part for the reasons outlined here, and in large part because there was no 'normal' represented in the DC/Marvel worlds. Superheroes exist in a world which is just like our America today, except that there are 12 thousand superheroes and supervillains, regular alien invasions, visits from Godlike creatures, etc... This, ultimately, doesn't really make any sense. Also lost is one of the appeals of any fiction with superheroes or the supernatural, the wonder of 'normal' people, the secrets and the revelations of those secrets. I get that maybe it's eventually time to let Lois Lane realize that Clark Kent is Superman, but when the whole world knows and accepts the existence of all this crazy stuff, and then basically goes about their business without much curiosity or wonder, then there isn't much space for curiosity or wonder for the readers, either.
...adding, I think one reason is that there's the temptation to do endless reboots and re-imaginings is that it gives them a chance to revisit all of the basic narrative arcs which are present for the characters/stories until things get too convoluted.
