As far as I know this is a physiology thing. Somehow the body cannot handle the low pressure above 25000 ft, even while having an oxygen mask on with 100% oxygen. Above 25000ft, there would be a need for pressure suits and pressure oxygen. Anyone able to confirm this for a fact?
Pressure suits are not needed , oxygen masks will do just fine.
Only above 60.000ft a absolute need for a constant pressure suit becomes an issue.