Kubrick kind of completely missed the point of Kings story and wrote his own shit instead with the shining as like the base outline. The point of the book was seeing the decline of Jack's mental state, and hiring jack Nicholson kind of went against that because he seemed kinda nuts to begin with.

I believe he also didn't like the way the stripped Wendy of most of her humanity and charecterizarion to make her the scared frail screaming lady

Kubrick version is a classic in it's own right but it's entirely understandable why King would be upset with it.