Hard to say. If that is the reason though, it is a real poor excuse.
I wouldn't say it's the sole reason but I don't believe it could be dismissed.
As the recipient in WWI of 2 DSCs, 1 DSM, 6 Silver Stars and 2 wound stripes, completing the war as the most decorated U.S. soldier yet being denied an MOH had to be significant to MacArthur.
Fast forward to 1942. Without getting into what Wainwright may or may not have done, MacArthur didn't ask to leave Corregidor, he was ordered to do so. Less than a month after he left and was replaced by Wainwright, Bataan fell and a month later Corregidor fell.
I can see where in coveting his own MOH, MacArthur felt that had he not been ordered off Corregidor, his name should have been the one nominated for that MOH. It's simple human nature.