I think that in most WW2 games most ppl want to play the evil Nazis. Not sure why. In COH2 a big reason is probably the fact that the Germans have all the famous tanks. Tigers, Panthers, Kingtiger, etc.
Germans are also easier to play with in team-games. Less skill required to win some games. Try playing Soviets in 3on3/4on4 and you will realize how hard it actually is.
In 1on1 matchmaking is usually more balanced by the way. Team-games attract the more casual types of players.
Soviets 4v4 is actually torture