Speculation is what built nearly every city including Shenzhen and San Francisco.

Building something from scratch whether it be a city, company, or even just an area of a city is often a risky endeavor. ROI horizons are long so there generally needs to be significant compensation for that risk.

Perhaps part of the problem in the US is it is not profitable enough to found new cities. We've capped the upside with things like statewide rent control and strict countywide zoning while also increasing costs with endless environmental reviews and the number of ways in which developments can be sued into oblivion.

If we encouraged more speculation and rent seeking we might have vibrant new cities.