Look at the current map list. The only tank maps are Leibisey, which was fought just days after D-day, so you won't really see fireflys or such yet. Plus, its against the Brits. Then, look at the other tank map, Luttich. Germans are attacking, plus its Americans, so no Achilles, or fireflies. Heavier Shermans, maybe. Meanwhile, the M5 saw combat in all those battles. Which is more important now?