I guess they just liked to marry other people from Ireland.
I have no interest in obtaining an Irish passport of citizenship. That country is more messed up than we are but we are catching up.
A friend of mine’s mother family came from Ireland. They were all Irish citizens for few generations before moving to the US. They did a DNA Test and it came back 0% Irish. Apparently, they did the same and married within the non-Irish part of Ireland. The Italian side of the family had North Africa DNA. Likely from the Muslim conquest of Southern Europe hundreds of years before.
Same here.