> You aren't required to pay for basic supplies, prison commissaries periodically give out hardship packages which include things like sample packages of soap and toothpaste, since withholding basic hygiene products is cruel and unusual punishment

You're describing the idealized scenario, which isn't exactly wrong, but it doesn't represent the reality that many prisoners actually live in. Yes, it varies - not every prisoner will have the same experience, even within the same prison - but having access to basic necessities is by no means a given in prison, and having wages garnished makes that much harder.

https://www.prisonpolicy.org/blog/2021/11/18/indigence/