You want to know the REAL reason?
Its because snipers animations are bugged to hell. Snipe, the #1 skill they have to use, is bugged so bad that it bugs literally every 3rd shot. And you have to use it a lot as it is your only spammable skill till later when you can combo followthrough. Even then its still your most used skill.
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Here are the other reasons:
1. They only have 1 viable tree for pvp AND pve(marks).
2. Their dps isn't top burst, and their energy runs out FAST(regens incredibly slow).
3. They are squishy in comparison to everything cept maurauder.
4. Cover is still bugged.
5. For utility or damage, sorc/merc is better.
6. They have horrible pvp armor.
7. Who wants to play a dps only class that has less dpds, utility, and survivability?