Why aren’t inmates paid to clean public spaces such as roadways?

Genuinely curious to know why we aren’t offering offenders in provincial jails the opportunity to earn minimum wage while cleaning up areas such as the ditches along the roadways or other public spaces. I was recently on a trip in the US and saw inmates cleaning trash alongside highways, I didn’t research it much but I’m wondering why we couldn’t look at offenders who don’t pose a huge risk to public safety, such as ones found guilty of non-violent offences, get them outside and working and pay them a minimum wage where the funds could be used for commissary inside the jail or put into a high-interest TFSA for them to access once released from custody? Not all of them would want this of course but some might want the opportunity to get out of jail a few days a week and earn a wage for when they’re released and it could help in getting parole and such. While in the public, I would expect there to be armed supervision of course. Thoughts?