Why Death Eaters Don’t Constantly Use Avada Kedavra
“Spells in the Potterverse require varying ranges of power, inherent magical abilities, conviction and concentration,” the user said, before backing up their reasoning as to why Death Eaters don’t constantly use Avada Kedavra. Their first point is that the spell is incredibly draining and hard to cast, much like the Patronus Charm, so wizards probably wouldn’t be able to throw it around whenever it suited them. It would probably weaken after each use, in fact, giving the recipient a “nosebleed” instead of ending their life. Plus, it requires such intense concentration that it probably wouldn’t work mid-duel, considering the hectic environment of a wizarding duel, and it also probably wouldn’t be your first instinct for that reason alone.
Beyond that, it’s possible that not every single Death Eater is skilled enough to even pull this curse off in the first place. As the Quora user says, not every single Death Eater is a rabid follower of Voldemort’s pureblood ideals aside from Bellatrix Lestrange, by far his most ardent follower. Essentially, using the Killing Curse all the time is, well, overkill — and probably impossible. “Using the Killing Curse throughout a duel when you aren’t exceptionally powerful like Voldemort or even Bellatrix is unreasonable and dangerous,” they concluded. “Not everyone’s a born killer or wants to be one.”