Firstly it was war time so the secret needed to be kept secret. Then it was after the war and everyone wanted to put the war behind them.
And I don't mean to excuse the fact that that it took so long for it to be recognized.
Only the first part of your comment holds water, it was wartime. Nothing else stands up.
No-one,least of all from what I know of them, the Americans, certainly not for fifty years or more.
I attended Battle of Britain memorials in the 1940s, books were being written, and films made, about Dieppe and St Nazaire if not in the 40s certainly in the 50s, and it is less than a month since Anzac day,which commemorates Gallipol, more than 100 years ago.
This was covered up because of gross incompetence, perhaps even negligence, in high places, at least as high as SHAEF, and maybe as high as Naval HQ Washington or the Admiralty.
At this stage of the war, just a few weeks before D Day, we had total mastery of the skied, and Allied aircraft roamed at will, and we had control of the Channel, we had to or D Day could not even be contemplated, as Hitler found in 1940.
How were these enemy vessels, not submarines or capital ships but lightly armed fast patrol' boats, which a single six inch shell would have sent to the bottom, allowed to get inshore on what should have been a totally secure coast?
Where was the air cover, where were the screening vessels? These ships did not blow up like the Hood, but sunk and there would have been people in the water. Where were the rescue craft which should have been available against just such an eventuality?
While Eisenhower is unlikely to have had any direct responsibility, he is unlikely to have kept his post if such a loss became known, and infighting was such that an acceptable alternative Supreme Allied Commander would have been argued over for weeks and D Day would have had to be postponed.
This was a high level and sustained cover up, maintained until the main protagonists were dead.
