Comics are a static and oddly conservative industry, at least as far as the dominant companies are concerned (not politically, but in the sense of "resistant to change"). It's hard to create new lead characters to add to the "pantheon." Characters don't change much or not for long. Family and children are problematic. So reboots, alternate universes, "what if?" stories and similar devices provide the variety that would otherwise be lacking. Of course, I am sympathetic to the idea that variety is lacking anyway, but it would be even worse if none of these types of changes were attempted.
Pop culture as a whole is starting to resemble the comics more and more in this regard, actually, with constant reboots and relaunches of existing properties that are already members of the "pantheon," rather than allowing existing characters to evolve or developing new ones. That is perhaps not very inspiring, but anyway it is certainly a dominant trend.