relating to this, but this isn't quite the cause
the real reason is because making comics and distributing them and getting funding has gotten easier.
think of it this way, If I wanted to make an independent comic book in the year 1990. I would have to literally compete with the big named comic providers, my only hope is to be really good and hope that a distributor gets me in or that I'm making a shit ton of comics to sell to newspapers and stuff.
With the advent of the internet in 2010, people who aren't necessarily talented can still be held on the same platform as those who are actually talented. Couple this with America's love of political correctness, all you really have to do to scam people out of their money is promise a less than mediocre comic strip that promises progressive liberal ideals, and people will read it and share it.