Yes, but Bish said he wanted them in-game. Moreover, they might not have been part of the 'real' eastern front, but they fought, together with the Germans, against the Soviets. There already is a Finnish map in the game, so it does not matter.
On the other hand, people really don't seem to get how much work goes into creating a faction. The answer is simple, no new factions. It is too much work. We find other ways to represent nations.