Chicken and egg. If you built the infrastructure beforehand, land prices would skyrocket because of increased amenity and then you'd have both excessive costs b

Chicken and egg. If you built the infrastructure beforehand, land prices would skyrocket because of increased amenity and then you'd have both excessive costs building in more density along with many people who paid top dollar for a "nice" suburb now losing out badly from planning decisions. Long term planning that is set in stone would solve this problem, but doubt it's politically feasible in many places.