A lot of criminals are victims of circumstance, and poor development in various areas, like social skills, and lacking pro-social behaviour, this is often learnt and or reinforce through various experiences.... and they reoffend because it continues in a cycle, and they go back to the groups they were in before, they cant get jobs, they are left bored, and idle... there's evidence to suggest reform is possible, at least in those who havent commited crimes out of pathologies like Anti-social personality disorder.
And yeah, I think the UK have some reform schemes, but they are ineffective
