The problem is, if you don't wan't people looking like "hobos," you'll have to establish some sort of standard to determine what beards are acceptable and which are not.

Simply stating "neatly trimmed" wont work very well, because one person's "neatly trimmed" is another's "hobo." It's a lot easier, from a policy perspective, to just say no to any facial hair or, in some cases, allow for mustaches.

There are just to many variables involved and there are more pressing matters for the powers that be to address.