It covers a ton of different storefronts that get maybe one sale every other month. Uploading to all of them individually would probably take hours. With those minimal sales that 10% is maybe, like, $5 over the course of a year, sadly.
Ooh, I see. If I had to guess, it's because folks who are into indie trans stuff seem to be pretty attracted to the idea of Itchio: it (had) good tools for discovery work like yours and covered more than just novels. Before the paypro stuff, it also started getting a reputation as the "hip new place" to buy books, so I'm wondering if it's that. (Plus, I've found that folks usually just like a place that's easiest to buy from and Itchio up until recently made it pretty painless.)