No idea, but the same applies to cars. We have motor cars which are powered by engines, unless they are electric in which case they are called motors. I believe that engines in America are called motors which further confuses the issue.
The difference I see between "engine" and "motor" is that motors always seem smaller. Motorbikes have motors, and they go "Bzzzzz". Vacuum cleaners have motors that also go "Bzzzzz". While cars and 'planes and so on have engines that go "Vrrrrrr".
On the other hand, really really big things have "power plants" that go "Mmmmmmmmm".
That reminds me of a story about a man from the middle of Sweden, Elis in Taserud. He was/is well known for his whit and sharp tongue. He has lived, he is not a made up person but perhaps some of the stories told about him are.
One of the men that had migrated to the US came back home to the village for a short holiday in the 1920?ies. Ha had done very well in America and had become rich and bragged a lot about it. When Elis showed him around in the village he said that his farm was so big that it took a whole day to drive around it in his car.
Elis answered: ?No big deal, we have got that kind of cars in Sweden too?.?
Is that a true story or do you have that replanted in UK soil also?