It won't happen every time. It only does a bullet cam when you hit their vitals.
What do you mean "only"? It's a sniper rifle! A shot can only do 2 things: 1) miss 2) pierce through skin, tissue and bone.
Also, sniper rifles are great support, but players never use them to their full potential. One of the reasons I love some FPSs is because snipers not only make a great back row support, but also a first rate infiltration unit. There isn't anything that provides a greater satisfaction than sneaking up on an enemy and humiliating them from behind.
Selfgratification is another reason why I don't play those games anymore. Not only can't you just walk from point A to B without being killed unless you check 523 possible sniper spots, but the guy who sniped you think he's the one humiliating
you when he shoots you in the back.