I can only speak for the Mennonite population that is my primary field of study.

First, I want to challenge the notion that Pennsylvania is predominately Italian-American. that there was a large number of Germans who settled in Pennsylvania during the first wave of German immigration, including various Anabaptists groups who were attracted to the colony because of William Penn's promise of religious tolerance. Land Agents of William Penn extensively recruited in the Palatinate. More germans came, forming the Pennsylvania German block (both plain dutch and gay dutch). At the time of the American revolution, about half of the Colony was ethnically German. (See John Ruth, "The Earth is the Lord's: A Narrative History of Lancaster Mennonite Conference). This population then moved west for motivations typical of the broader American population: a need for farmland that was increasingly unavailable in the East.

There was also a second immigration of Mennonites who came from Prussia by way of colonies in Russia (1870s and a second wave 1920s) who settled predominately in the midwest because of the availability of good farm land (leaving Russia for religious reasons).