Comic books have always been political, especially books like Captain America with the Nixon thing mentioned a while back as an example. I not too knowledgeable about politics, but Marvel was built up by liberals so I don't get that complaint when it comes up.
Because now there's people of color and women that are leading it and the typical white male audience doesn't like dealing with the idea that they might be racist/sexist whether or not they're aware of it. Not to mention that LGBT is rising more to prominence.
It's easy for that demographic -- white heterosexual males -- to immediately feel like the finger is being pointed at them. If I recall, there was a study a few months ago (there was a thread on it, but I can recall) that basically said "whenever issues of race are brought up with white people, they immediately get really defensive as if they're being accused directly." I would imagine the same thing happens with males and sexism, and/or with heterosexuals and homo-/transphobia. And since white heterosexual males are still seen as the majority demographic when it comes to comics, all of a sudden things are "too political."
So that's why it's a big deal now. If that makes sense. I'm trying to keep from getting longwinded (I get kind of aimless) and sounding ignorant.