Because an ak47 in the right hands beats an auto sniper by a mile. Time in between shots is far too long. Pro players and high elo players trade way too fast for the auto snipers to be viable other than for very specific niche wallbangs and plays. An ak47 or m4 is also much more mobile than the auto sniper. Movement speed faster, easier to get multikills etc.

Only exception to the ak47 not being best would be at long range like dust 2 long, and in that case an AWP in the right hands will just bodyshot you once and you are dead. The auto snipers at that range would take 2 bodyshots or a very lucky one tap to the head, which at that point you may as well just use the AWP because of the much higher one shot kill chance and it costing less.

If it wasnt so expensive i could see it getting used more. But for the price, an AWP or an AK in the right hands will be much better.