This memorial is part of a group of memorials in Normandy devoted to various aspects of D-Day and its aftermath including an Omaha Beach Memorial Museum which is dedicated primarily to the American effort. The sector around Bayeux was the sector manned by commonwealth forces -- nearby is the commonwealth cemetery -- just as the American cemetery is near the Omaha Beach Memorial Museum. The prominence of different flags at different memorials is perfectly legitimate.
Prominence I could understand, such as setting the British flag prominently at the British beaches, the Canadian at the Canadian Beach, etc. That honors the men who landed and died there at that particular beach.
But the complete absence of the American Flag, with the presence of the other three? And a conspicuous hole where it once flew? That's an insult.