Even if the IP is continuing to be used by the original creators, they can set the "canon" while competition might force them to do a decent job of using the IP in future.
For example, the Matrix. It had definitively entered the cultural meme pool after 20 years. If other creators could make money telling stories from that universe - whether through images, music, video - then the populace at large wanted that content. And if film number 4,5,6 are any good they make money as well.
Even if the IP is continuing to be used by the original creators, they can set the "canon" while competition might force them to do a decent job of using the IP in future.
For example, the Matrix. It had definitively entered the cultural meme pool after 20 years. If other creators could make money telling stories from that universe - whether through images, music, video - then the populace at large wanted that content. And if film number 4,5,6 are any good they make money as well.