The uglier you are, the more niche your kink has to be to get you laid. Say you're an attractive person who's really into something super weird, like sploshing or some shit like that. It's going to be tricky for you to find a similarly attractive person into your weird kink, so therefore you widen the pool. If you are so niche that the only person into your specific thing is a fat fuck, then this is where adverse selection comes in. Fatties realise they can shag much higher quality by getting into stuff that attractive people don't have to do to get some.