According to this post by the Science Fiction and Fantasy Writers of America guild, it would appear that The House of Mouse feels that when your contracted screenplay novelization writer is fighting stage 4 cancer, that's a perfect time to not pay him. Alan Dean Foster has written a ton of such novelizations and sparked the Star Wars Extended Universe with "Splinter of the Minds Eye." Elsewhere I've heard that their alleged reasoning is they purchased the rights to, but not the obligations for, said novelizations. They're running the production companies as wholly owned subsidiaries and have not just purchased specific properties, so I don't understand that reasoning.
Alan Dean Foster and SFWA President Mary Robinette Kowal discuss the non-payment by Disney of several contracts for works including multiple Star Wars and Aliens novelizations.