Because otherwise I am not seeing it.
Sounds like they were grossly underprepared. Probably not proper mountain wear. You sweat on the way up and get soaked, even in breathable Gortex. Then you stop moving and BAM hypothermia sets in with the wet clothes. It doesn’t matter if you have the jacket or not.
The only hope was getting to sheltered trees out of the wind, taking off clothes, hugging under the bivouac sack and space blanket, and covering yourself with tree boughs before crawling in the sack.