> want to question the assumption here that "pioneer mindset" is an inherited trait

About half the variation in personality traits is biologically heritable: https://www.bbc.com/news/uk-politics-55834023. Even political ideology is moderately heritable: https://www.sciencedirect.com/science/article/abs/pii/S23521...

On top of that, there’s social transmission of values within families. Much of the country descends from 20th century immigrants, where the effect of the immigrant generation is still prominent. Much of the rest of the country descends from people who left their civilized east coast and settled the frontier.

> Rather, the vast majority emigrated because it was literally the only way to move up in a world where land ownership was the key to wealth

This isn’t any different in much of asia or africa today. Most people are content with their place in the world without abandoning all their kinship ties to “move up.”