[AnthonyMouse]

Alice doesn't want to build it because if she doesn't she can afford to build twice as many housing units on the same lot, which is worth more money even without parking spaces, and the building doesn't need such an expensive foundation if it doesn't have to support a multi-story parking structure in addition to the housing units.

Bob wants to build it on the next lot over once he sees these new buildings going up and is willing to bet that the new residents will generate demand for parking, and can choose how many stories to make it based on the local demand for parking, which is based on numerous hyper-local conditions that are best evaluated by the owner of that specific lot and not just based on how many housing units are in each building.