I’m not familiar with the process, but could there also have been a fraud aspect (not copyright) to this that wasn’t worth the effort required to prevent? Upload “songs”, generate lots of listens, get paid.
An older acquaintance of mine is a professional musician living in Nashville doing commissions.
He made a track for a trailer of a video game, but chose not to publish it on Spotify (for reasons I don't know). One of the fans ripped the song from the trailer, uploaded it to Spotify, and was collecting all the royalties.
Even though Spotify keeps taking it down, someone else uploads it again, ad nauseam.
Something like the Amazon ebook scams:
https://www.zdnet.com/article/exclusive-inside-a-million-dol...
https://www.inc.com/minda-zetlin/amazon-book-stuffing-author...
Nothing wrong with it, just lack of foresight on the uploaders' part.