Caveat: this is not a good explanation, and deliberately avoids most of the nuance.
WOTC licensed the core rules for 5e (a small fraction of what's contained within the player's handbook) in a way that allowed third-parties to release content designed for 5e. Then they changed the licence in a way that would require every third-party to pay them significant royalties. They said it wasn't released and they were gathering feedback, but they were also telling people to sign it. It seems to be a money-grab by the parent company Hasbro (which also owns Magic the Gathering).
Paizo came out with the ORC licence which is held by a trust, is irrevocable, and has community support.
I need to edit this for my upcoming BG3 playthrough with my mates... No idea what image to use though