Adding onto to the promotion aspect, bad promotion can lead to a BL seemingly romanticizing harmful tropes. There are some BL that bank on being problematic, and you can tell it's supposed to be this way because it's not labeled romance, or there's another genre like horror/drama/thriller. So the readers can pick up on that or the author is going "oh yeah no, this isn't a healthy relationship".
But then you get promos that make those stories seem romantic?
It's weird -- and exactly the thing that happened to Killing Stalking. It was BL, but the main tag was psychological horror. It had the atmosphere of most of the horror/thriller comics on Lezhin. And it got promoted as a romance BL. Granted, pretty sure the author made some bank from that, but they also had to tell people "no, this isn't actually a sweet romance. It's not even healthy. They're both kinda shitty people"
So that definitely adds to the confusion, especially when readers go in with that assumption. For someone like me, I'd be able to tell "yeah, the promo kinda botched that". But for some readers (some younger readers) will take that promo to heart, base their experience from reading other BL (that may or may not be dubious) and try(?) to find ways to claim it's ok?
A lot of things get messy with a vague/misleading promo added in the mix. Definitely something I've seen in other genres, but I definitely notice it in BL/GL comics. Even with the romance comics with the CEO tropes. Doesn't really make me wanna read them, if the promo is that bad.