[jabbany]

PVP and leaderboards attract a different audience than normal gacha players which is why it tends to be rare-ish in gacha games. (Almost none of the popular ones focus on it).

Most of the time, the social aspect of gacha is to show off your "collection" rather than to show off your "skills", so adding PvP and leaderboards doesn't do much for most players. Instead, gacha games tend to have "social" features that do let you show off your "collection" in some way, like profile cards with character showcases, "supports" mechanisms that let friends and strangers borrow your characters, or sometimes just blatantly a score for your gallery completion %.

Also FWIW, Genshin actually has PvP, it's just that it's only present in the card battle mini-game. And my impression (could be inaccurate though) of that is most players are not particularly "into" that mode.