They basically allocated a pot of money to pay the people they have harmed off. But these people had to actively go out and request their conviction to be overturned. Which of course many people were reluctant to do, since it means they would be upturning their life again, and going to court and finding lawyers and etc. They understandably have very little trust in the system. So Post Office just shrugged and decided they don't need to keep that much money around.
Even crazier. The Post Office just recently lowered(!) the amount of money they allocated for compensations: https://www.bbc.co.uk/news/business-67784706
They basically allocated a pot of money to pay the people they have harmed off. But these people had to actively go out and request their conviction to be overturned. Which of course many people were reluctant to do, since it means they would be upturning their life again, and going to court and finding lawyers and etc. They understandably have very little trust in the system. So Post Office just shrugged and decided they don't need to keep that much money around.