From a WHM PoV :
It is way easier to start an AoE pull with Holy compared to "wait 15 seconds for your precious Blood Price" then Holy.

At the start :
1) You have stoneskin up.
2) Most tanks pop mitigation during the end of the pull, right before the AoE hell is unleashed.
3) With proper timing, Holy will land the moment everything is gathered (means those mobs lagging behind won't have a chance to attack the tank and is stunned straight away).

After "15 seconds for your precious blood price" :
1) No more stoneskin.
2) No more mitigation (You can pop more, but good luck with the next pull!!)
3) Everything and its mother is hitting you at full force.

And for those that believe your AD spam > Holy Spam damage, that's nonsense and any non mathematically challenged person can see that.