"Religious persecution? Really? So starvation, wanderlust, adventure, or anything like that played no significant part in the population of the country?"
Well, it was usually persecution of SOME sort that drove them: religious, political, or economic, and it applied a lot during the American expansion. Irish immigrants and the like moved west to Kentucky and so on in response to the Whiskey Rebellion (political persecution--taxes). A lot of the Mountain Men were escaping past lives or trying to make a living when there was none back home (economic). Many were fugitives escaping prosecution. A lot were being enticed by offers (many of the wagon trains were formed for this, and there was the Homestead Act).
Wanderlust and the like probably enticed some people, but the vast bulk of immigrants and pioneers had simpler motives: either a reason to go somewhere or a reason NOT to stay home.