Why do women wear those tight clothes at gym?

Why do women wear tight clothes at gym? Even when they're not slim and good looking?
Do they need to expose their rolls over their bodies as some sort of proof or excuse for being there? I don't want to see it! Why don't they wear some large loose clothing (as I do)?
I only want to see nice looking people when I'm training. If I see fat people spending a lot of time exercising and they're still fat, then I don't want to exercise!