A great book on this subject is Ulster to Carolina: The Migration of Scotch-Irish to Southwestern North Carolina, by H. Tyler Blethen and Curtis W. Wood. To briefly summarize, the Scots-Irish living in Northern Ireland were actually Protestant lowland Scots living on rented land provided by the British government. The British rented the land to the Scots in an attempt to infiltrate Northern Ireland culturally by offsetting the balance in favor of Protestants over Catholics. The problem for the Scots-Irish living in the Northern Ireland settlements was that for the most part the land could only be rented for up to thirty years. After thirty years if they were unable to renew their lease they had to move, thus traveling to North America became a logical choice to many of them. The reason why they chose the Appalachia region was because of the time in which they arrived in North America. Most of the coastal region was already inhabited by English settlers, forcing new settlers further inland. The Germans settled in most of the land outside of the cities, think Lancaster, PA, which meant the Scots-Irish had to travel further Southwest in order to settle new land. Therefore, most of them ended up in was the Appalachian areas of North Carolina, Virginia, and Eastern Tennessee.

Long story short, they did not necessarily seek out North Carolina, but rather it was the region with the most available land in the early to mid 18th century.