That’s because when you watch the film on cable, they cut the sides of the image off to fit it on a 1.78:1 TV screen.
The black bars are normal and every movie with an aspect ratio over 1.78:1 will have some level of letterboxing (black bars) on the top and bottom, and every movie with an aspect ratio of less than 1.78:1 will have some level of pillarboxing (black bars) on the sides.
Thanks. All I know is that I always have and always will find the black bars at the top and bottom distracting. Gotta zoom in slightly.