I remember the glory days of them in the 70s and 80s.
There would be the novelization. Then the YA novelization. Then the photostory. Then the photobook. And then the audio storybook of the movie (on an LP) with a book.
Terminator has an American novelization and a British novelization. Written by separate authors.
It used to be routine for me to see the movie and get the novelization. If only I'd watched more movies but I was never a big movie goer.
The book doesn't change, but the reader does. Or it may be that the comfortable familiarity is the point.
From age 12 to 19, I read my copy of Watership Down to ragged edges. At age 19, I got a rabbit. A free roam house rabbit. And I've never been able to read Watership Down after that.