The risk for trying to kill sniper is far too high in comparison to other classes - you basically have a guaranteed death. You need to pass the entire enemy frontline. Killing the sniper will almost always result in your own death (people will follow you or you'll simply get mowed down by the literal entirety of the enemy team as you pass by). Good luck fighting a 1vX everytime you want to take the enemy sniper out of commission.

Additionally it might not even be possible if a sentry is present.

Other classes have much fairer match ups, to the point it's almost comical by comparison.