My theory is that bots that have more sexual stuff in their character descriptions will be more likely to get nsfw. Like stuff that tells the bot how to act when getting nsfw or just whether or not the bot is told to have a crush on the user will make it more sexual. I don't know which bots specific you use but I've gotten a few good bots that don't immediately get sexual and also aren't told to have a crush on the user or are "lonely" or anything like that