Typically, the only people who got onboard with American colonization wanted to get rich, had nothing left to lose, were convicts so didn't have a choice, or were actively facing persecution back home.

Not really people one would want to pick for a generational ship.

And comparing colonization of the Americas to a generational ship is disingenuous. It was still possible for them to come back home. They even maintained allegiances and contact with the homeland. The reason colonization even kicked off after the initial successful colonies, was for economic exploitation; something that won't be possible with generational ships.