Shane said it himself, manga has "something for everyone". American comics are virtually dominated by one thing for a very narrow range of customers which is getting smaller all the time.
There's manga geared towards pretty much every demographic in a wide variety of genres, available weekly (in Japan anyway) and for a cheap price. The stories are easy to get into because they're almost all kept in print and even the most popular ones have an ending. They aren't 70 year old trademarks fighting the same fights over and over with zero stakes storytelling that can't even kill a side character or let any change stick because it's a 70 year old trademark that needs to stay the same and the ever aging manbaby audience likes the status quo to return eventually. Reboot, rinse, repeat.
Mainstream American comics are creatively bankrupt because they aren't outlets for creativity, they're work-for-hire life support systems for ancient properties that are far more successful as movies than they've been as comics in
at least a decade.
Warren "Internet Whorin'" Ellis wrote about this wretched development
20 years ago in a piece called
"The Old Bastard's Manifesto", which contained this snippet later used by Bendis in an issue of
Powers:
The whole thing is worth a read. Ellis was ahead of the curve on a lot of ideas back when he still had ideas, even acknowledging he was part of the problem since he would deride publishers for pushing out superhero pablum right before accepting work from those publishers to produce more superhero pablum. He championed the manga model before most stores were carrying manga. And he's absolutely right that American publishers making what are ostensibly kid's comics for an overwhelmingly adult audience is not helping anything, but slowly choking the industry to death.