Disney changed the whole focus of the story to be about Mr. Banks and his conversion from a proper British banker to a feel-good Americanized father. It's true that the original books don't have a strong story arc and are mostly a collection of separate incidents, so they needed something to tie them together.

There seems to have been a lot of that going around. Rilstone did a good long filleting of the soap opera family drama that the movie added to The Lion, the Witch, and the Wardrobe.

I don't remember the name of the film expert who said the whole unifying focus of E.T. was Eliot's alleged conversion from tactless to tactful!