The population of Ireland is around 5.3 million. More than 6 million people have immigrated to the U.S. from there. Factor in kids, grandkids and such... It makes sense that there would be a number of people claiming Irish heritage. Also the number of people who find an Irish accent attractive is non-zero.

Edit: a quick search found 9.4% of the U.S. population is of Irish decent. (Mixed obviously). So more Irish than all Asian decents combined if I read it correctly.