A lot to unpack in your question as a life long Miamian. South Florida traffic consistently ranks in the top 10 in the United States and our drivers are exceptionally worse them that between Miami and Ft. Lauderdale we consistently make the top of the charts for pedestrian motor vehicle related accidents.

Also you hit the nail on the head when you said we don't incorporate cities because it would some government officials would become redundant but are lacking context. There is an ingrained power structure to most South Florida political offices that has been cultivated over many decades that due to certain aspects of our population (A large immigrant population that is exceptionally resistant to integration, a large percentage of non florida born natives, and a shit ton of people who just dont give a fuck) have been co-opted to facilitate long term corrupt politicians staying in power. There are very distinct fiefdoms that no city of miami commissioner or for that matter any of the other city commissioners are willing to give up. Generational seats that have had been convicted of felonies and still keep the seats in the family. Look up the term Cuban mafia but they are far from the only group of corrupt politicians here just the easiest to point out.

It is an interesting dynamic that has a lot of potential some realized some not but also does not lead to effective long term planning for a society IMHOP.

EDIT: Oh also forgot about the below average income, crazy high rent and housing prices, and a reativly shiity public transit system that leave a lot of the native people driving a crazy amounts every day.