Not everyone lives in their car where having a mattress at the ready is the ideal solution.
Many of us travel to destinations with a few hundred pounds of "gear" and utilize the "cargo" area for "cargo".
Having a mattress in the way exacerbates loading/unloading of "gear".
Thus, having something that folds up and out of the way during such travels allows for said "gear" to be easily accessible, loaded and unloaded.
There are many ways to skin a cat.
Not that I've tried.
But, I have the "gear" to do so.