You're browsing the GameFAQs Message Boards as a guest. Sign Up for free (or Log In if you already have an account) to be able to post messages, change how messages are displayed, and view media in posts.
It's because flinch is relative to the amount of zoom your sight has. If a sniper scope flinched the same amount a RDS flinched, it would jump wildly from the sniper's point of view, and be much harder to deal with compared to an RDS user. So essentially, snipers get free flinch resistance instead of having to deal with that.