ELI5: Why is it magically ok to blatantly steal someone elses song and make money from it, just by slapping the "cover" label on it?

You still have to pay a licensing fee to the songwriter to record a
cover.  However, there’s a clause in copyright law that provides for a
“compulsory license” for recording covers, which means that the
songwriter isn’t allowed to refuse, and the fee that you have to pay is
fixed.

Explain Like I`m Five: good questions, best answers.