the raid game changes pretty dramatically after tier 10 or so, and there are many situations where anyone in the raid can die instantly if they mess up, and having a 30% chance of them being saved is... well, one of most important buffs anyone can have.
it also becomes harder & harder to deviate from healing the tank at high tiers, often times i simply cannot stop healing the tank to heal my group, and beads/cc pants/heal pots etc become a huge part of the game. it's not uncommon for me to tell someone on vent or whatever there's no way i can heal them and they should do whatever they can to save themselves. beads are also insanely powerful on a tank, especially if the raid is proactive about recasting them, so the tank can use them liberally to keep themselves from falling low.
the value of both of these cannot be understated, and keeping your group prepared is one of the most important roles of a raiding cleric. not casting them isn't a realistic solution. yeah.. and besides, the 15 sec recast on DB does no good other than wasting time. i can't think of a reason why this exists. i can see why they wouldn't want a group version, but i don't see the point of the recast