So in the civil war union snipers and crackshots were given green uniforms. So that brings up a question: Why weren't all soldiers given green uniforms? Wouldn't it make more sense to give every soldier a green uniform so the overall performance of the army increases?
No because the Nature of Warfare of the time, as well as for the several millennia before it, required commanders to visually see the total or majority of the army to effectively direct battle.
Camouflage had its place in battle but only in limited specialties. Sharpshooters preformed specialized tasks.
10,000 camouflaged men deploying like sharpshooters would be less affective than 10,000 uniformed soldiers because the enemy would use it's collective firepower and communication to smash through the battle line and surround pockets of sharpshooters who can't communicate with each other and form a cohesive defense.
Think about it like this. A cannon is far more powerful than a rifle but it wouldn't be effective to give every soldier one.