It's all about cost. There have been several articles on HN discussing the problem. One in particular (I think it was a study done in Michigan) stated the average citizen in that city would need to pay an extra $7K in taxes just to break even for existing infrastructure. (ie.... all new projects are halted)

EDIT: It was Louisiana and the cost was $8K, here is the study. https://www.strongtowns.org/journal/2017/1/9/the-real-reason...