Meh, I am cool with adult comics. I am even okay with those being the focus. Sure, kid comics should be a genera, but "kid" comics occupy an eyeblink of time for most people. If you are consuming other media, especially books, it doesn't take long to realize that kids stuff is, well, kids stuff. I know that as an avid book reader I more or less skipped the entire YA phase. I wanted more complex and interesting stories and was going to gouge out my eyes if I read one more awkward coming of age story.
Kids are plenty coddled and protected from all the imagined evils of the world. Coddled people grow up into dysfunctional and boring people or go through a true and rather traumatic "coming of age" when they hit the real world. Yeah, handing a kid a full on rape and torture porn comic is probably a bit much, but something with themes that a grown adult can appreciate? Awesome.
If you want to see a real stark difference, read golden age comics and compare them to golden age sci-fi books. The comics were meant from kids, and sci-fi was for adults. The comics suck and are borderline unreadable because they are shallow, cliche, and meant for kids. Some of that sci-fi on the other hand has survived half a century of wear and tear and is still relevant.
On a more practical side, adults have money. I never read comics when I was a kid. I considered them to be, well, kids stuff. I stuck to books and consumed hundreds of thousands of pages. It wasn't until I was an adult and armed with wads of cash that I gave (adult) comics a second look and realized that some of it was good and interesting. I can offhandedly blow more cash in a day or two what I could have scrounged and begged and pleaded for as a kid in a year. Appeasing adult nerds who tend to have STEMish jobs is a pretty solid business plan.