This explains the difference. The European method seems the most optimal.
On the other hand, I don't think Americans ever pick up food with their fork and switch the loaded fork to the other hand, especially if the food is scooped, not speared. A lot of food would be dropped in the process.
As a non-conformist, I taught myself to use my knife in the non-dominant hand so that the fork is used in the same hand regardless of knife usage.
Or, it could be what my English son-in-law does, he uses his fork and knife, in different hands to aid in pushing food onto his fork. (He's right handed, not that it matters in this case.)