If it looks like a bigger, buffer descendent of the vehicle that it's replacing, that's fully intentional. When the Pentagon needed a way to cart troops around through dangerous terrain, it first turned to Humvees carrying more armor. This slowed down the vehicles, which were designed to be light weight, and didn't offer as much protection as needed. Next, the military looked to MRAPs, a kind of heavy truck made for surviving bomb blasts. The L-ATV borrows design elements from MRAPs, but with the promise of more speed, and therefore more mobility, than the heavier armored trucks. The original Humvee, like the jeeps it replaced, was designed as an off-road vehicle, and the L-ATV should be able to travel freely across terrain too.