Why does the shelf have an upstand at the front and a downturn at the rear?

Both 6mm folds add stiffness to the platform. The front edge turns upward, while the rear edge turns downward.

The front upstand also gives a small amount of resistance to something sliding forwards; the rear downturn leaves the back of the platform open for equipment that extends beyond the shelf.

Neither fold should be treated as a positive equipment retention system.