Predators mostly kill their prey quickly probably because they are really hungry! And it gives them less chance to get away. Simple as that.
As for the crabs - Norway must have too much money in its coffers to spend on crabby thoughts. How the heck....I mean c'mon ! I can tell them now - their main thought would be "OUCH!" That probably just saved a lot of dollars.
If it bothers you - chill them down in the freezer first. But who says this is comfortable either? Maybe that should be researched too
I dunno - things were simpler when we went crabbing on the beach in flip flops with all the relatives, got bitten toes, sunburn, then boiled off the crabs in a massive pot and had a feast, then washed off in the sea and a great day was had by all including the seagulls (except the crabs, naturally).