Oh don't get me started on this one! Argh!
LOL. I can get quite worked up about this myself!
In real life, I often see attractive, fit women with overweight (not morbidly so, but noticeably) out-of-shape men.
It's on TV because it's believable.
Very few women choose physical attractiveness over other attributes in a long term relationship, and very few women are willing to end such a relationship simply because their boyfriend/husband has let himself go.
For women, relative physical attractiveness is a bonus. For men, it's a sine qua non. Has been since the beginning of time.