> why can't we find ways to build new areas they want to live in?

Because people want to live their lives today, while what you propose takes decades and must be a process worked on by Town Halls, not "the people". And no, it's not the same. The Town Hall of rich people who didn't yet have the need to leave, is dominated by rich people who didn't yet have the need to leave, not the people who is more affected by the excessive centralization.