I personally think that anime and manga having a ‘pipeline’ helps them.

• A publisher like Weekly Shonen Jump shotguns a load of new series into their comic and sees if any stick.

• If a series is popular, then their individual volumes sell well, encouraging WSJ to continue publishing.

• After a while, the popular series will most likely be given an anime (which nowadays tend to be very manga accurate), which tend to export better.

• If the anime is popular, volume sales increase worldwide, and you have a massive hit.

While this quite effectively creates new popular series, it leads to a massive manga graveyard.

Western comics don’t really have this kind of pipeline and I’m not aware of any WSJ-like publications for new Western projects.