J_A_B,
My guesses would be along the following lines:
1: The don't turn well at all andmost people like to turn.
2: They are German and that incurs a usage penalty. However much you, I and many others don't connect the aircraft to the Nazis, many people still do. Japanese, Italian and Russian aircraft also suffer penalties for different reasons. As the N1K2 and La-7 demostrate though, if an aircraft is user friendly enough the penalty can be overcome.
We know that the Fw190D-9 and Bf109G-10 are harder to get kills in, and that is what it boils down to. Ease of survival is a very distant second in the priorities that determine what aircraft get used most. Because of that, famous and exceptional TnB, cannon armed aircraft will be the most common. The two most common BnZ, the P-51D and La-7, aircraft can both turn adequately.
That is my theory anyways.