It's sort of a sliding scale between: making content that is popular enough for a platform to make considerable revenue from it and wants to pay you a portion to keep you there, because your content is competitive and could be making other platforms money. Or, it's a free hosting site for data you're uploading that's funded with ads. Every other platform I know with this model, like Youtube or Twitch, have a cutoff between the two, it's a hosting site for users until they're popular enough to become business partners with a monetary agreement. It's two way freedom between each party, spotify doesnt have to pay anyone anything, and no one has to host their content on spotify.
This isnt a retroactive change of terms, it's new terms starting next year. Everyone's getting what was agreed to this year. If they dont support the new terms, they can leave the platform. They wont, because they're using it as a free hosting platform and not a money maker, maybe with hopes they'll be popular enough someday.