Because the Israeli army is often involved in very dangerous close-quarter urban combat, having wounded or incapacitated soldiers is bound to happen, and evacuation is often very problematic. To put it in perspective, it can already be difficult to navigate urban terrains when fully-loaded with weapons, ammo, water and other gears, so transporting a person on top of that may at least take out another soldier (if not two) from the fight, and that can be extremely dangerous if the tactical unit was small to start with.
Ubergizmo, Israeli army's Injured Personnel Carrier is a human backpack
