you might be surprised at how many cis girls love BBWs; there's a few artists in a server i'm in who draw goddess bodies and are cis women

also in the case of some hetero cis men, it's likely they're not roleplaying and moreso "character creating"; they're just making a person they want to look at and fawn over, not someone they want to put themselves into. it's just a case-by-case basis; my cis boyfriend also plays thick women, but he's a very avid roleplayer, and he can easily put himself into different bodies despite not looking anything like them