Why would hundreds of people go to the lower populated and more expensive worlds to buy things?

Even if they couldn't go the most populated and cheaper ones, they can still go to the ones a step below. And it's not just those lower pop worlds I'm concerned for. I'm concerned for the entire economy as a whole. Higher pop worlds will have their cheaper items bought up, which will inflate prices, and lower pop worlds will have no one buying their stuff causing deflation. The hope is, of course, that it all balances out. Until then, lower pop worlds will have to adjust to not making as much, and higher pop worlds will have to adjust to spending more.