Natural selection. Because predatory bugs would approach from the back, hoping to surprise and to kill the victim, the appearance of the rear-facing scoops makes the VMax bug appear to be bigger and more-ferocious than it really-is. Thus, the predatory bugs left it alone.
Some insects use protective concealment, like the Walking Stick, while this insect has appearance-deterrant physiological structure.
I've missed that pic, a good one! Now I know what bit my wallet repeatedly.