They were used later in the crossing of the Scheldt eastuary. The reason for all of Hobart's Funnies, was for specific purpose. The DD was because a gun tank was considered esential in the first wave. LVT (Didn't the British call them Buffalo?) didn't mount the firepower. Also the early version didn't have a ramp, so jumping over the side made you a sitting target. If you also consider that Normandy was landing onto a flat beach, unlike the Pacific Atolls, and LCI could get more men in faster and out of the boat via the front ramp quicker. LCI were also easier to build en mass, and probably a lot cheapear.