Why do these people hold on to their heritage so strongly. People 4 or 5 generations deep still saying that they're Irish or Italian?

I'm from Ireland and Irish Americans are laughed at over here, we call them Plastic Paddys. The come over here talking about their families and their homeland. For instace my last name is O'Connor and I had a yank woman ove here one day telling that we're related because she had the same surname.

I've heard that deep generation Italian Americans are known as wonderbread wops in the States.