For the same reason big hair can make someone look crazy. They make you look unkempt.

Currently travelling and managed to get my beard in check almost a week ago. Will probably be untouched for another month. My hair is also getting long. I’m afraid of weirding people out but every time I get a haircut and beard trim + wet shave they always make my beard too short and it’s annoying to grow it back to how I want it. I generally keep it reasonably short and neat but let’s see what happens after this next month of travel.