I've wondered why both styles of flatware use have persisted, thought it might have something to do with the development of the fork in America vs Europe (kind of prongy spoon vs. kind of knife you can scoop with respectively). That turns out to be incorrect, but instead, the 'knife/fork swap" style seems to have been a class marker in high-society French around the time of the American Revolution (possibly brought back by Franklin or Jefferson but there's no evidence) and we Americans never switched back.
I went to school in Normandy, picked up non-swap there. It works a lot better in situations where elbow room is restricted, which might have something to do with why we in the land of huuuge houses haven't picked it up.
Also, I've seen a number of English folks using their knives as something to bring food to their mouths. People in Normandy did *not* do that - but I remember watching in fascination as an English student at my university scooped up loose items on his knife, put that in his mouth. 'Fascination' because I was waiting for something to drop. Yes, it was rude of me. I'm an American and know no better. :-)