Comfort, mostly. ITOVs are hot, cumbersome, and can weight upwards of 50lbs on their own, with full combat load (6 30rnd magazines, radios, grenades, first aid kit, water, the list goes on). If you could transfer the armor and load carrying from the person, to the exoskeleton, it's less stress on the soldiers.
And if you make a soldier stronger, well armored, and mobile, you increase their combat effectiveness by a shit ton. And if an armored exoskeleton soldier is as effective as, say, four soldiers without an exoskeleton, then you can reduce the amount of manpower you need. A squad can do the work of a platoon. A platoon can replace a company. A single battalion can be as combat effective as an entire brigade.