Airport (1970) and Hotel (1967), both based on books by Arthur Hailey.
Hailey could tell a gripping story, but gosh, it took him a long while to get there. I particularly recall three pages of backstory about the airport insurance salesperson in the book Airport, which added little to the story. In the movie, it was taken care of quickly and easily (there was a company sales incentive happening, which resulted in Guerrero buying a more expensive insurance policy with pocket change), but in the book, we follow the salesperson’s life, from childhood to her job selling flight insurance. Totally unnecessary backstory, IMHO.
Same thing in Hotel, the book. Three pages on the backstory of the guy who sifts through the hotel’s trash, looking for silverware. All we need to know is that he finds the note from the Duke of Croyden, and we get that in the movie.
Hailey was incredibly detailed in his books, but the producers, directors, and screenwriters of the films wisely decided to get rid of Hailey’s details, and instead, put out entertaining films that moved along at a pace that audiences could follow without falling asleep.