Because the change to orbital in PvP was a change that hurt a class that was already fairly balanced, and made them weaker in rankeds. OS/Flyby was used as a deterrent to keep players off the sniper/slinger but since OS/Flyby barely even tickles anymore, it is no longer a deterrent. Overall, snipers didn't need a nerf, and this mostly hurts their survivability.
The main issue is with PvE though, as stated above.
Try to keep up, kiddo.