The reason there is no MACR is because the crash occurred in an area where the US authorities had access and the aircraft was not missing, and so there is a Form 14 (Report of Aircraft Accident) for the loss instead, which is listed. The photographs of the crash site are marked as having come from the accident report.

I have only seen wartime deaths of US service personnel registered before the US entry into the conflict and the Isle of Man. It would appear there was an arrangement made to exempt the US services from having to register deaths in the UK for the duration. Post war, and I am not entirely sure when it occurred, deaths began to be registered in the UK.