Because it would be extremly OP.
3v3 forexample. Rogue Fights 2 Range Dps, 1 Healer.
Rogues team is Rogue Rogue Disc Priest.
OP team is Wlock SP Resto Druid.
Wlock sends in pet, both rogues gather 5 combopoints quickly, re-stealth, Sap both dps and Open on the Priest - Priest = instant Death.