> Sentences can't be extended without additional convictions.

This is technically true but substantively false. Fixed duration sentences in most US jurisdictions (life sentences are different) are come with essentially automatic substantial reductions for good behavior which are removable for poor behavior with minimal process, avoiding the hassle of judicial process for offenses in prison, and frequently “refusing work” is a cause for removing those reductions.

So, technically, its not an “increased sentence” for refusing work. But, in practice, that’s exactly how it functions.

>This is technically true but substantively false.

Only for a certain mindset of people, who feel entitled to every possible bonus ever mentioned. We might even guess your age from that alone.

>which are removable for poor behavior with minimal process,

Once convicted you are subject to administrative punishments. Don't be convicted.

>So, technically, its not an “increased sentence” for

You misspelled literally. It's literally not an increased sentence.