If snipers were 1 shot kills on body shots they would still be less effective in the average situation than shotguns or autos. If people are tired of being sniped all the time, fair enough, but that doesn't mean that rifles are easy to use. People like using them specifically because they are difficult to use. It's a lot more fun getting a really clutch shot than it is getting easy kills, it just feels pointless after a while. With a sniper you get high rewards, but the price is the high amount of time and effort required to master them. People who like a challenge are naturally going to gravitate towards them, and just happen to get really good.