It is more nuanced; the private investors want to make profit as quick as possible, they do not care about long term development of the area (many politicians either, they might not be in their position after next election).

The private investors won't do infrastructure either - it is expensive - so they want to build where the infrastructure is already in place. So that's why we see trying to increase density.

So the zoning rules are there as a conterweight to this.