Well, I guess unless Jon said “I saw the NK just raise his arms at Hardhomme and all the dead just popped right up” maybe they didn’t realize it was that easy. Jon isn’t completely stupid though. He should have thought of it. Or Bran. I’m sure he looked in on that at some point. I was surprised no one thought to grab a torch and start burning them though. However, I guess if they HAD done that in such an enclosed space, everyone might have died of smoke inhalation or ended up burning alive.