A crossbow would be a bad weapon. An actual crossbow takes a semi-long time to reload and it really just wouldn't be able to compete with weapons like the M4 and BAR. If it had a faster muzzle velocity then other weapons ingame, that would only give it a slight advantage and would still be outgunned for the most part.
stfu people who say era isn't real life, you can't have a crossbow that's shoots fast even if this is a game.