Hey! As someone who enjoys the fat ugly bastard trope, there are a few reasons I think. One of which is, it's unrealistic. The odds of your SO falling for, or sleeping with, such a person compared to your typical stupidly handsome and jacked dude are pretty low. Another, which builds on that, is its an added layer of humiliation. Seeing someone, a powerful/authoritative woman, arrogant woman, demure woman, etc., sleep with such a character is top tier. I personally despise the handsome trope, which I find is significantly more common than the ugly bastard. Especially if you want a good game or hentai. Those are the top reasons I can think of off the top of my head. Then again, maybe it's different for the other connoisseurs