Just Curious, Why can't guys wear flats and gladiator sandals?

Ok, so back in the 1920's and 30's guys wore flats and women wore heels. Out of curiosity I tried on my girlfriends flats (plain black like guys in the 20's and 30's wore) with skinny jeans and they looked ok on me. During the Roman Empire guys wore gladiator sandals also. Some were short (ankle height) and some were tall (knee high). Again I also tried on my girlfriends with skinny jeans and shorts. I was curious cuz girls always say how comfortable flats are to wear. My girlfriend and I are basically the same size, I wear an 8 in Vans,converse and Uggs and she wears a size 9/10 in the same shoes so we swap different pairs. My girlfriend didn't think the flats or gladiator sandals looked that bad on me. She thought the gladiator sandals if they had thicker sts would look more like they were for men to wear. Now I know why so many girls wear flats cuz they are ez to put on and really comfortable. The gladiator sandals were'nt bad either and comfortable. I guess curiosity got the best of me. What do you girls think? BTW im 15 and my girfriend is gonna be 15.