Bills to pay, snail mail to open or making a shopping list, the task the human is attempting makes no difference. It is up to the feline to sort out the mess by walking all over the foolscap and if need be, flopping right on them.
This may annoy the people but that is unimportant to your cat. They have a job to do and do it they will. Their assignment is to get in the way and I know of no cat who does not excel at this mission.
And if you think you can outsmart the pet by forgoing paper and using a computer. Think again! It is just as easy to plop onto the keyboard!
Cats win! Every time.