Only lower security prisoners are used as firefighters, and there is still a substantial amount of supervision involved. CA has a lot of wildfires and needs a lot of firefighters. It's a dangerous job and few are willing to do it, while the pay isn't that great for such a risky job. So they've got two choices: use prisoners for close to free labor, or pay firefighters more to attract more hires. I'm sure there's the occasional escape. Here's a news story about one in 2021: https://lawandcrime.com/crime/california-prisoner-steals-fire-engine-tries-to-escape-custody-while-fighting-wildfire-video/

They went with the cheaper, vastly more unethical option.