In addition to your reasons, and sibling's 'easier to get up', I'd add:
- does actually look much more comfortable than the ground to me. The middle would give a bit into the cavity of the base, it's not just a sheet on the ground as I imagined reading your comment.
- being raised makes it easier for medical personnel to attend to any injuries etc.
- looks like a more clearly delimited arrangement, I imagine it would more easily become difficult to walk around people sleeping on the floor, as they'd sprawl out, lose the organised grid arrangement, etc.
But I don't have any relevant experience to comment on how important any of that is, or if it's the best way to spend whatever cardboard beds cost in such a scenario.