> it sounds like some legal jester dance done to entertain [...] copyright laws

Clean room implementations are a jester dance around the judiciary. The whole point is to avoid legal ambiguity.

You are not required to do this by law, you are doing this voluntarily to make potential legal arguments easier.

The alternative is going over the whole codebase in question and arguing basically line by line whether things are derivative or not in front of a judge (which is a lot of work for everyone involved, subjective, and uncertain!).