This is for balance. Snipers have no place in a regular MP style game because their useful range SHOULD be way too long. However they shoehorn them in because players like them and variety is good, but they ahve to nerf them somehow or they'd be overpowered.
Only BR type games have the room for proper sniping. And yes, a .50cal anti-tank rifle should be 1-hit killing anyone no matter where it hits. But having a weapon like that in a game can severely ruin the experience for all, so they nerf it and make it take multiple body shots. This rewards players with good aim that can land headshots on faraway targets, but allows for players to escape death if they are hit with bodyshots. If it was 1-hit kill everywhere, it would just turn into a sniper campfest where everyone sits on rooftops with HDRs and no one ever moves, ever.
What they should be doing, IMO, is completely nerfing the ADS times for snipers. If they made it take 3-4 seconds to fully ADS that heavy obtuse weapon properly to your eyeball, that would make them completely unusable in any kind of short/mid-range situation. Whereas right now you can just quick scope and get away with it if you're accurate. This would relegate snipers to solely long range engagements, which is where they should be used. This would also give snipers a choice to make with their secondary - since they can't use the sniper mid-range at all, they'd have to decide between carrying an SMG for CQC or an AR for mid-range, and realize they'll be out-gunned in certain scenarios depending what they choose.
In the same vein, they should be massively increasing recoil for all weapons in general. I'm tired of seeing people beam players at midrange on full auto with an AR. If recoil/kick required you to semi-auto from mid-range to long-range, that would let snipers have a more distinct advantage in longer range engagements. It's crazy that you can get away with running an AR/SMG Loadout in a BR game with a huge open map. Sniping should reign supreme if you're at longer ranges and deter moving through open fields.
/rant