Her dad bod boyfriend wont stop her to get railed from the ripped dude during summer vacation.
I also would pick as a gf a girl which is in shape but is not a top model yet I would still bang the top model, the fact that I dont consider a too hot girl reliable doesnt stop me to have sex with her.
Its not exactly insecurity but more like a clear cold evaluation, the hotter your partner is the more work you have to put on it and the higher the changes of a bigger better deal coming and stealing.
Unless of course you are a famous rich athlete with a top body, in that case get as a gf the top of the top and relax.
So its the same old story, they pick a guy which is gonna support them with low chances of cheating or leaving her while keeping their options open.
"oh no no sorry hot guy but I only go for bad bods".