why do most guys find girls with long or medium length hair more attractive than short?

In most cases it is a culturally learned preference. In some cultures, eating a spider is a delicacy. Why don't all people think eating a spider is delicious? Because they are not from the same culture.

Medium Length Hair Guys

Long hair just is! With long hair you can always wear different style or curl it or straighten it. And hair looks really pretty when it blows in wind. and short hair is more common for dudes then for girls so sometimes people would think the girls trying to be boyish and not girly. Once I saw this couple and the girl had shift hair and someone thought they were gay. Lol also boys love to grab the girls hair you can't really do that with short hair

Medium length hair because it is easy in order to handle and you can still do most of the hairstyles

Cause a lot of guys think that long hair is more feminine than short hair.

Longer hair looks sexier to men. They seem to dislike short hair because it is not feminine.

Long hair is more feminine. You can run your hands through more of it and it looks more natural

nicely short hair makes you seem much more clean and it makes you seem to be like you have a good feeling of style and long makes an individual seem more manly and playful