At the end of the day, whatever the source file looks like, you’re turning it into an analog signal in order to make the speakers move. So how is it at all effective?
You can even send a digital stream of the bits over Bluetooth to speakers. So it seems like the ability to decode it is a fundamental requirement for it to be a useful file. So why even bother? It seems like it would be trivial to copy into a different format.
DRM for music is largely a thing of the past.
As to why it ever existed, company executives, they saw piracy and wanted to try and stop it, thats it.
DRM for music was never really effective.