I'm a guy, and I have no idea what patent leather looks like (except for maybe those lovely knee-high boots ladies wear). So basically, I don't know if they look good as a belt or not. Maybe they do, maybe they don't.
However, Blu_IN does point out that it does take a while for ASA to change the style. Think of how long we had those button-down shirts that looked like something from the 70s.
The answer, in my opinion, is that one proper uniform (minus any chest protectors, masks, etc.) costs around $150 (slacks, shirt, hat, belt and shoes). Many umpires, like myself, have more than one complete uniform (I've got 5 uniforms with two extra shirts that I took out of the rotation). Would we really want to have to keep changing the uniform once every couple of years? I know I certainly wouldn't, and that's why I take such good care of the ones I already have.