To the downvoter: I don't know what more you want. That's the synopsis. The density is too low, so they don't get enough money to sustain themselves with all the infrastructure that is required to have suburbia
This means that they exist because they're being subsidized by revenue collected from elsewhere, such as from cities.
Whether this is fair or exploitative depends on how you figure the math for "it's being collected from people who live in the suburbs and just happen to work in the city."
The question is how long they can keep taking out more and more debt against the promise of never-ending growth and income from one-time development sales. The answer probably isn't "forever".
https://www.strongtowns.org/journal/2019/11/21/choose-your-f...