If I had to guess, I would say that the mossie isn't seen as much because of two main reasons:
1) Not many know what its capable of, and of those that are, the mossie is too difficult for them to bother learning. They would rather fly something thats easy to fly and land kills in.
2) Since the Mossie is seen as an easy kill by many (I share that view, if you don't be stupid, and don't bump into an ace), the nature of the MA means that you're almost guaranteed to meet an enemy who is hell-bent on killing you. If hes any good, you probably won't be able to keep ordnance during the fight. That means that you've lost most of your capability as an attack aircraft (all you have left are the guns), and that even a 109G-2 with a 500lb bomb would have been better for doing damage to town.