You're assuming that those local businesses can just spin up and wait what, months? years? for the density to reach levels that will sustain said local business

You're assuming that those local businesses can just spin up and wait what, months? years? for the density to reach levels that will sustain said local businesses. Most people don't have the money to throw down the drain like that merely wishing for the urbanist utopia to arrive. In the real world, money matters, timescales matter, customers matter, etc.