I just wrote in a comment to a blog about North American fork usage, I think I should just go to bed or something. There was lots of mystified pondering on the subject of why americans switch their fork to their left hand when they’re just eating with a fork, and people saying things like it being an older etiquette tradition that only the right hand delivers food. I can see that being true, history has a strange aversion to left-handedness. Case in point, in choir today, I conducted a piece, and one of the tenors noted that I conducted southpaw, and as I sat down, reassured me that many great people are left-handed, himself included (I laughed rather derisively on the inside).
Me, I think the modern convention is really just because most people are right handed. I’ve never heard an adult tell a child who kept their fork in their left hand to switch to their right hand, but I have heard parents tell their struggling right-handed children that it is perfectly acceptable to switch their fork to their right hand when not using a knife.