The Ash12 recoils so hard, it can only be used on semi auto (shooting full auto on factory staircases does not mean its working). And because the bullet flies really slow, it is hard to use at a distance.
This means the ash12 is stuck being a close range weapon anyway, so why carry that heavy thing around if you can get a revolver with the same ammo for a lower price?
The Ash12 has 10 and 20 round magazines, however a single 20 round mag will likely cost as much as a rsh12. And most fights that last longer than 3 shots with an ASH12 means likely the ash12 operator is dead, so the higher magazine capacity does not help that much.
The gun has minimal recoil on full auto in real life:
The ash12is not supposed to be a "cool meme gun". It was designed to end a fight in one shot and deliver very high damage in urban combat while bein subsonic. In EFT it can not do that. The damage system keeps a player functional until he is completely dead, so a player could take 3 hits from it and survive it.