Great question. They crumble because their power ( or rather perceived power) is taken. They become vulnerable. They become the target or victim in prison quite often. That said many, when they adjust, become very dangerous prisoners as they lack empathy and will often attempt to build a power base in prison and target the weak in there also. the variables and environment just changes.
If you google you'll find lots of stuff on this that reliable and valid. Journal articles. GBC is an unknown entity. Stress is a big factor. Hence my term house of cards. Hope this helps