That might have had to do with getting the troops ashore at specific windows in time related to daylight and tides.
The US learned a sad lesson about those tides the year before at Tarawa. They needed an extra high tide to get the landing boats over the reefs surrounding the islands. They miscalculated the tide and got a lot of men killed. The boats were bottoming out on the reefs and were sitting targets for Japanese gunners. My uncle piloted one of them. He got his boat in and unloaded. On the way back out for another load, a motar round landed in his boat. He spent the next year in a hospital.
I know nothing about the beaches and sandbars at Normandy but misreading the tides can be deadly.
