Why do men say i should be a glamour model?

I'm 17 and i want to have a career in health. Most guys when they ask what im studying they think its either hair or beauty. And some men say i should just be a footballers wife so i wont have to do anything or become a topless model or something along those lines. It really makes me angry and feel insecure that men think this of me and probably lots of other girls out there. Why?