unfortuantely, many of the times female personalities have that whole primadonna attitude. the show has to be 'all about them' and when it's this way, its just not funny. you usually end up with that whole self-absorbed routine which no one can relate to, which ultimately sucks all the entertainment value out of bits/breaks.
other than having the token mid-day female jock or the female morning show sidekick, women jocks don't seem to sell in radio.
call me sexist if you want, but women typically just aren't as funny as men, if they were, we'd have more female stand up comics, or a larger amt of succesful female hosted radio shows for that matter. the proof is in the pudding.