Is it because fat girls are easy?
If only. Try convincing an archetypal "easy" fat girl to do it with the light on or let you play with her belly or refer to her as "fat" without sobbing and trying to throw up the nice dinner you bought her. Spend weeks convincing her you're Not Joking, your buddy's not gonna jump out of the closet with Tucker Max and a camera. Cave and show her your porn collection one night just to draw big red circles around You Not Joking. Watch it backfire into sub-issues like Am I Too Small For You or Do You Only Like Pears. Never ever let her find out what "hogging" is. Fat girls are just as complicated and frustrating as any other earthling.