I really don't get how some peple say that non-Sharp specs require no Cover. You don't use Aimed Shot as DF/Sab? It's our hardest hitting ability, no matter if you're specced into Sharp Aim or not.
I'm pretty sure those other abilities have some secondary effect that works on normal mobs, but not on playes, not the ability itself.
As for the reason...
It would give more burst damage than the PvP is balanced around.
I would rather prefer some kind of traps available to Sniper/GS. Mines for Sniper, tripwires for GS for the flavor.
Stealth is OP's thing, Snipers take up a position and unleash hell, and traps would go along with it well.