It may be becouse im a graphic designer and years of working in the field mixed with education in the fine arts academy thought me one crucial thing: There is a time and place for everything. Manga is not a universal style, it's a style that carries a specific history, connotations and semantics that appeal to specific people and by that extant specific clients.
Cd project red wont hire a manga artist to work on witcher because it carries different semantics, esthetics and mood, they'll go looking for a semi realistic or realistic fantasy concept artist or painter. A book company looking for illustrations for a book about Warsaw city wont hire a manga artist because it would feel out of place, they'll go to an illustrator with a graphic design background. A magazine about social and psychological issues wont hire a manga artist because it wont appropriately express the gravity of an issue, instead they will probably also gravitate towards someone with a unique style that will probably accompany those themes better.
As for the art schools discouraging manga style: it's not that they don't see it's potential, i's becouse they want their students to develop their own styles and valous not to adapt manierisms of others.
Weather you think so or not manga is a very specific art style and even by borrowing parts from it you are making a statement which sets you to a specific path. Even when a manga artists decides to partake in more serious themes they're either trying to be more realistic like Junji Ito or they want contrast for shock value (madoka, higurashi, fran etc.)
Which leads me to another thing that i learned as a graphic designer: It doesn't matter what you think it looks like, what matters is how your client or demographic perceives and reacts to it. There is a perfect little anecdote / example: If you take four "L" letter's and try to make a logo out of it by putting them together at 90 degree angles in a windmill pattern it wont matter that you know it's four L's, other people will see a swastika. It's best to look outside of our own comfort zones and little worlds so we wont be eaten by our own egos and mannerism.