Leo Family - Patrickswell

My Great Grandfather was John Leo, middle name perhaps Daniel. I believe his  father was Patrick. John Leo married my great grandmother, Julia Hastings. I believe they were from Bruff. They emigrated to the US and my grandfather, Patrick Daniel Leo was born around 1883 in Natick, Mass, around the Boston area. At one point, John left the US and went to Australia where it appears most of his family emigrated. Julia Hastings Leo died around 1898 in Worcester, Mass. I know Leo is an unusual Irish name. I am trying to research the family and wondered why John left the US and left his wife and 3 children to go to Australia. I just visited Ireland on a tour 2 weeks ago so I didn't have the opportunity to visit Limerick.