What drives people to steal from charity shops? Maybe a 'risk assessment' tells the perpetrator that charity shops are 'soft' targets or that low value theft means less severe punishment. Or maybe it's a short-cut for people who need those items? Many people would rather risk being labelled as thieves than admit to needing charity.
Is it easier to take than to ask? Probably. It's certainly quicker and you're not risking a negative response. Is it less embarrassing to steal anonymously (unless caught, of course) than to be recorded as a 'loser' who needs charity? Certainly in some people's opinions.
It seems that the decision to shun help from 'do-gooders' and resort to law-breaking may be based on retaining what little pride is left by keeping their anonymity. I'm so lucky that I haven't had to find out for myself.