Because Germans have the advantage in speed, and boom capabilities. British planes don't even get a decent speed up until the cannon typhoon, and even then the Germans already have you outclassed in climb rate and armament. Not to mention the bombers are literal cloth so any chances of making it to the base without relying on puny .303s are low at best.
Its like British is really good because of the amount of guns it has in the beginning, but as history goes on its like Churchill didn't give a stuff about planes (Excluding the Spit.IX with its 14 sec rudder turn time, which is being fixed soon I assure you).