Interesting point, Jim D. I think it might be because many of the people who crossed oceans were running, hiding, escaping, or convicted criminals. (Also, a lot of names were changed by the immigraton authorities because they could not spell Gaelic or Italian, or what not.) Immigrants often preferred that people on their new continent not know just who they were when they left the Old Home.
Me, I can name 5 GG's, right off, 2 more if I went and looked it up. My dad always said he was Scots/Irish or Black Irish. I don't know for sure, but I ASSUME Co. Kerry because that is where many of the Plantation Scots of Ulster went when they were fed up with being Planted. My mother's name was Brooner, with oomlahs (sp) over both the O's. She said it was a Dutch/Fresian spelling of the German Bruner.