Mostly because Operative/Scoundrel are the most mobile healing class and the least dependant on interruptable cast times and therefore harder to shutdown.
With the addition of vanish, they're the most survivable healer.
1vs1
2.5k Single hit
5k Single hit
75k damage
300k damage
Killing blow
2.5k Heal
5k Heal
75k heal
300k heal
10 kills
25 kills
I don't know the objective points or protection numbers.