Here’s an argument:

Every suggested buff to the A1-S that I have seen on this subreddit would make it a far better weapon than the A4 in most scenarios. More ammo in any way would make it a better spray weapon than the A4. ROF buffs would make it a better spray gun than the A4 (see 2015). A damage increase would make it better than the M4 in every way. Armor penetration increases would make the gun better for spraying.

The reason many people do not use A1-S is because they choose to try and kill multiple opponents from the same angle with a spraydown. The A1-S rewards positioning yourself in such a way that you get the single kill and then change angle, with spraying as a very last resort. Thus in most people’s experience, when they try to use the A1-S like a A4, they see how useless it is for that specific job, they assume it’s useless.