I think they are used as cheap/cliche click bait. There are a ton of young readers that want to read “bad boy” stories because media sources make them seem “hot, aloof , dangerous or taboo”. It’s a cheap way for authors to ensure these young readers read their stories.
Not to mention that, at minimum, 90% of the “bad boys” featured in stories on this app are cold and abusive. But given the pathetic excuse of " he’s a douche but its because he had a bad childhood"… lots of people have bad childhoods. This is not an excuse for verbal or physical abuse to the MC or anyone else. (slight rant. I think these stories, when done incorrectly,(most) are quite damaging to the perception of young, impressionable readers.)
Personally, I think a story where the good guy/sweet friend/nice guy gets the girl because he treats her with respect, protects her when needed and isn’t a stereotypical douchebag would stand out as far more unique and interesting compared to the thousands of “bad boy” stories on the app.