Crabs and shrimp have it worse, for crabs you need to cut off their face for them to actually 'die' humanely. Ripping them to pieces doesn't do it fast enough. Shrimp there is no efficient way to do it and in some countries its actually a common street food to eat them raw and alive in a bowl with sauce/alcohol on them, that particular dish is called 'jumping shrimp' or 'dancing shrimp', squid go through this as well where they're throw in a bowl alive, alcohol is poured on them, and you eat raw.
Lobsters their anatomy just makes it tricky, you have to knife from behind the head and quickly slam it down fowards, if you're not using sharp tools or strong this can be slower than it needs to be but it is the most immediate kill if you can. Yes there's a nerve that runs down, but all you want is the animal to not be conscious. Some parts of the world actually illegalize killing them any other method in restaurants so chefs learned how to do it quick.
Personally I love seafood but will exclusively purchase frozen from the grocery store, I just wish there was more meat on cold lobster tails, it feels more complimentary to a steak than a main course with how little there is for the work involved. I did once make the almost-fatal mistake of keeping a cold lobster tail in the fridge for a couple days and then cooking it, I was not aware lobster tails had to be from store to oven else they spoil, I'm glad I just had an upset stomache for a couple days and didn't really register I gave myself food poisoning.
