>"Why would someone in their right mind think working on the Voyager project could damage their careers"

Assembly? Understanding how things actually work? No Agile? No K8s? No Rust, No React? - death knell for someone's resume

>"and the person will move on to another space exploration job, with the extra golden star of having been on the Voyager"

this is the best case with the result of being tied to another single project for years and unemployable anywhere else. in more realistic case - warm goodbye in few years and start your life from scratch with no credits for the thins done.