On earth, populations move to new regions because of 1) natural population increase and gradual migration by people who are pushed out of their home region due

On earth, populations move to new regions because of 1) natural population increase and gradual migration by people who are pushed out of their home region due to overcrowding, or 2) deliberate conquest by groups with a very centralized power structure, in which there is a person or group who is in a position to extract tribute or resources from the conquest. In the case of interstellar travel, neither of those two are feasible. The people doing the migrating have to be supported by massive amounts of money, which rules out the first reason for migration, as it’s not a cost efficient way to deal with overpopulation. And there is no way to exert control or exact tribute from light years away, so that rules the second reason for migration. So there is a question of motive: why spend the money when you will not directly benefit?