Why do cats like cardboard boxes?

[Catherine]

Maybe it is the thrill of sleeping on something breakable. Cats love things that break.

There is no challenge to a soft comfy bed. There is no human reaction to sleeping in a soft comfy bed. 
Maybe the trick is to put the soft bed in a difficult spot and tell the cat not to go there. 
As kids were told not to take vegetables from the garden which guaranteed that we snuck and ate veggies all summer long.