Funny that we can't compliment a girls ass

I was at the gym the other day and was "casually" strolling past the room where the girls have their aerobics/boot camp/dance classes. I was admiring the sights which included perfect asses tucked into yoga pants, flat stomachs, amazing legs kicking in the air etc.

I couldn't help but think how its funny I can't tell one of those girls "wow, you have an incredible ass, good work!". I'd be kicked out, possibly even reported to the police. But it would acceptable, if not welcomed, for me to say "you have beautiful eyes" or "thats a great smile". An eyes and a smile are total luck of the draw. The girl either had good genes, or just got lucky that the hue of her pupils is considered attractive.

But a perfect ass- that takes hard work and discipline. She has to go to the gym, eat right, do research, and stick with it. But we can't compliment the great results of hard work.

I know, I get it. Looking at a girls ass is considered sexual and inappropriate because society has deemed it so. But its just funny when you think about it how its ok to praise random luck and not hard work.