WHY NOT Ireland? A lot of people who've come over here have had contact with Irish physicians in the past and think it'd be a cool place to study medicine. A lot go for the cultural element as well, people go because they want to experience european culture. And, some people have "Irish roots" and want to be near family/friends. And question...WHY would we WANT to be taught in the American system? okay, obvious answer is that those of us looking to practice back in the US would feel "safer" with an American system. But truth be told, that's pretty bunk. Medical education is for the most part, standard - you learn the same anatomy, the same physiology, etc. so not following an American system doesn't really hurt us. US/Canadian Irish IMGs do very well in the match and on the USMLE. Many US IMGs will do rotations and electives in the US to get a feel for what it's like. There may be a transition period where US IMGs may have to adjust to practicing back in the US, but people catch up very quickly and this doesn't present a problem.
It gives people like me a chance to live outside the box that is the US for awhile, while pursuing medicine. I personally didn't apply in the US because the thought of studying in the "American system" depressed the hell out of me, and have found an alternative that works wonderfully.