I can understand missing it pre-flight and taking off, but for the life of me I can't imagine not noticing the climbing cabin. I have taken off in a 737 with the packs off and I had felt it, looked up and identified the problem, and made a decision not to say anything about it until 500ft, all before the gear was up. It was that obvious. I didn't have a cold or restricted sinuses either.
Hopefully that doesn't come across as 'look how great I am', ( I was the idiot who got distracted and left packs off), the point I'm trying to make is that it is incredible that they didn't notice the cabin climbing. Any thoughts on that? Was it some sort of low climb rate with a hold down or something?