Dollar a day isn't much but at the same time, they don't want inmates making a ton of money in there. Not just to save the state money, but because if inmates start having large sums of money, it can cause more violence, drug trade, etc.. Also, prison isn't supposed to be a pleasant place. Working creating office furniture and etc. gets a lot of hardened criminals in a work-ethic routine and tries to encourage them to work when they get out of prison instead of falling back into crime(which is often the case). Less then a dollar a day can get them commissary privileges like other kinds of food(in some facilities.. such as soup), hygiene products(because they don't want the inmates to feel like prison is a free place to live. They don't want inmates to think, "why get out and struggle when I can just do something and if I go back to prison then so what, things are free and easy".

So from the outside of the facility, yeah it looks like the state is just trying to use them for slave labor, but it helps in a way. There are other detention centers that have very comprehensive work programs to help inmates learn actual skills they can use on the outside in factories and etc.. They're actually good programs and are designed to help inmates change their outlook on life.