Here’s a thing about the death curse. You have to mean it. If you don’t, it won’t work. Even the Dark Lord (who loved to cast the spell) did not use the death curse at Snape while killing him. Perhaps his respect for Snape would come in the way.
The Curious Case of Severus Snape: The Hateful Soul Who Sacrificed Everything for Love
That's amazing! I haven't thought of that.