In general when you're a "prisoner with a job," that's slavery, even if there's some pittance of a wage involved. They're paid $10 a day, let's not pretend this is a fair wage for a fair day's work. This is a form of economic warfare against the working class, who shouldn't have to compete against prison labor.

They also get reduced time. Considering the program is extremely sought after, I think it should continue in light of the fact that its literally what they prefer compared to not doing anything

I don't have a problem with the program, or any prison labor program, as long as it's paying at or above market wages.

We sanction Chinese companies for using prison labor in their products because it's ethically wrong. We shouldn't be engaging in the same practice we sanction other countries for.

Depending on slave labor from prisoners also creates a conflict of interests for society because it creates incentives to imprison people rather than prevent crime. It should never be a smart financial move to imprison your citizens.

It's very literally slavery. You don't have to deny it because the practice is legal in the United States. As you say, they can do this work or they can sit in state prison. I don't have to squint to see how that's a threat. These prisoners didn't volunteer to be in prison. If you gave them the choice of fighting fires or going free I doubt many would pick the $10.00 a day firefighting gig.