Suppression grenades are probably the exact reason you can't throw a grenade from inside the bubble...it's risky enough to kill a defender in or near a bubble as it is, you shouldn't be able to extend your near invincibility offensively as far as a grenade throw especially with the distance you get with the grenade throw gauntlets. It would be ridiculous, everyone would just run full teams of St-14 defenders with maxed int/disc and just sit in bubbles w/ shotties throwing suppression grenades everywhere.