Why does the definition of fair use remain ambiguous?

Millions of dollars in legal fees have been spent attempting to define what qualifies as a fair use.

There are no hard-and-fast rules, only general guidelines and varied court decisions, because the judges and lawmakers who created the fair use exception did not want to limit its definition.

Like free speech, they wanted it to have an expansive meaning that could be open to interpretation.

Learning about them i guess, idk