How are you calculating how expensive a suburb is to maintain versus a city? A suburb can't exist without a city, basically by definition. A city would have fewer wealthy commuters without the suburbs, which would reduce the size of the economy, but ultimately a city can exist without suburbs albeit in a diminished state. You cannot say suburbs are cheaper to maintain than cities when they cannot exist without cities.
While it is true that wealthy people live in suburbs and commute to the city and contribute to the economy, the same infrastructure is generally more expensive in a suburb than a city because it has to travel longer distances between houses. That is just geography and physics. Picking up garbage for a building with 10 apartments is going to be cheaper per household then driving between 10 different houses, for example.
The relationship between cities and suburbs is symbiotic in some ways, but in many ways suburbs rely on exporting costs onto cities. Suburbs exclude poor people by design (zoning rules and housing supply restrictions), so that they don't have to pay for all the social services used by poorer people. And when you say 'city infra is more expensive', a huge percentage of the city infrastructure (e.g. roads, trains, sewers) is used by people who commute into the city when they are in the city. Very few people living in the city go and use infrastructure in the suburbs on a daily basis.
Imagine if everyone in NYC tried to move out to the suburbs, it would not be remotely feasible. They wouldn't have the social services for the poor and wouldn't be able to get the tax revenue to maintain infrastructure between houses while preserving the spread out distances between houses without dramatically raising taxes. The rich would then probably just flee somewhere else and take their taxes with them. Additionally, lower income people couldn't even afford the houses/cars needed to live there in the first place.
While it is true that wealthy people live in suburbs and commute to the city and contribute to the economy, the same infrastructure is generally more expensive in a suburb than a city because it has to travel longer distances between houses. That is just geography and physics. Picking up garbage for a building with 10 apartments is going to be cheaper per household then driving between 10 different houses, for example.
The relationship between cities and suburbs is symbiotic in some ways, but in many ways suburbs rely on exporting costs onto cities. Suburbs exclude poor people by design (zoning rules and housing supply restrictions), so that they don't have to pay for all the social services used by poorer people. And when you say 'city infra is more expensive', a huge percentage of the city infrastructure (e.g. roads, trains, sewers) is used by people who commute into the city when they are in the city. Very few people living in the city go and use infrastructure in the suburbs on a daily basis.
Imagine if everyone in NYC tried to move out to the suburbs, it would not be remotely feasible. They wouldn't have the social services for the poor and wouldn't be able to get the tax revenue to maintain infrastructure between houses while preserving the spread out distances between houses without dramatically raising taxes. The rich would then probably just flee somewhere else and take their taxes with them. Additionally, lower income people couldn't even afford the houses/cars needed to live there in the first place.