Cub:

Apparently, one of the reasons for 25k is the slower onset allows (in theory) one to learn to recognize their own symptoms.

The other reason: as a new USAF student (30 years ago, next month!), we did a rapid-decompression ascent to 35k, if I remember right. But they stopped the 35k profile a few years later. A student either got hurt, or died from some reason....LOC, evolved gas; I never got the full story.