Queen Elizabeth II surely preserved it but if you want to know why the British Royal family became beloved look no further than America and Elizabeth's father King George VI and mother Elizabeth visiting Hyde Park for 4 days in 1939 at the behest at FDR. No reigning British monarch had ever visited the US and at the time there was no love lost between the common people and the UK. FDR and King George knew that had to change with the rise of Hitler so FDR suggested that in lieu of the King visiting Canada, he visit FDR in Hyde Park, NY.
The Canadian PM also attended the event (he thought it was a good play too and was more than willing to come to the US for the state business he had with the monarchy) as did press hand picked by the FDR administration. The goal was to King George and his wife come across as regular people and to that end it worked. FDR famously served hotdogs at the event and the headlines screamed "King tries hotdog, asks for more" and spoke about how the royal couple drank beer and ate hot dogs alongside everyone else and to their credit they really did spend time with regular people, many were civil servants in FDR's government but even so.
FDR and the King and Queen got on really well. It was the beginning of "the special relationship" between the US-UK and it really helped to humanize and endear the British royal family with Americans who until that point had been cold (some downright hostile). As odd as it is to say relations between the two nations were nothing like they've been since.
At any rate, I shudder to imagine how the world would've turned out had this high stakes picnic not happened. It is a large part of why the two nations were able to trust one another so much during WWII and obviously helped with everything from the initial lend-lease push to later war efforts. Obviously, it helped a great deal that they spoke our language but the relationship that started with some letters followed by some hotdogs changed the fortunes of both nations.
Without this... Five Eyes (US-UK-CAN-NZ-AUS) surely never happens and the war goes very, very differently.