Maybe this is why Manga outsells comics. Now, if they'd just release a Detective Chimp manga...
That's just the tip of the iceberg for why manga outsells. part of it is vision. Heck even their work for hire stuff is usually the product of a single creator (with some assitance of course) working on one series and one story that doesn't interact with any others at a time.
Basically there is a variety of genres and tones which is always a plus. The age range for the stories that it does is wide as can be and in addition there is consideration given to a general audience of young and old alike. At the same time theres also stuff that is meant to zero in on a specific demographics. You get alot of bang for your buck per volume. A collected manga volume might be about 20 bucks but look how much comics you get for your 20 bucks.
The stories and series have beginings, middles, and endings. A complete experience. Even when dealing with long running franchises like for example Gundam, because each new incarnation has it's own identity and run which completes. Eventually giving way to a new take that is sometimes radical, somtimes traditional, sometimes both. Yet for the most part the same themes remain for each generation to experience for themselves.
So even if you don't like a version of that franchise that is currently running it will end in a short amount of time and things will move on. In addition, nobody has to feel shafted because whatever version they did like they are left with at least somekind of real closure for. Which makes things much easier for the reader to take or leave whatever comes after that.
It also helps to that the Japanese are less prone to just throwing whatever is old away. Having a sense of history is very important.
Also while you certainally have creators who like to spin things in different ways or analyze and deconstruct genres, you have just as many who are playing along with their genre just fine and just trying to do something entertaining with it. Rather than blaming the genres tropes or the characters or the audience for bad sales.
You also get something that the best superhero comics are really good at doing which is stories where you are getting a mixed bag rather than sort of stewing in one tone although there are certainally manga one can go to for just emersing themselves in a mood or just seeing something totally bizzare. I mean in the same story you have about a giant robot you might have comedy, maybe even a little tragedy but you also have drama and romance and tales about the virtues of freindship. Of course this can sometimes backfire to where the tone is so all over the place you can't get a grip on the series identity.
At the end of the day manga succeeds because it's a variety of genres for a variety of audeinces doing what they are each best at instead of one genre (superheroes) trying to do be everything for one audience and losing what IT is best at in the process.