Exactly, Tolkien also got paid, but no one could claim he did it for the money. Both hid and the work of his son to preserve and share his legacy were labors of love.

For something completely different, but the same here is a YouTube clip of Billy Strings playing with his dad, a very similar dynamic here: https://youtu.be/_6U6NCvOfl8

I doubt the sum total of royalties for the work released by Christopher Tolkien amounts to even a single percent of those for the Hobbit and The Lord of the Rings, even if you include The Silmarillion. He could just have leaned back and counted the checks incoming.

£100,000 in 1969 is nearly £2 million today, so while little compared to the billion dollar adaptations in the 2000s, still a tidy sum