Maybe i’m wrong but one problem is that flight sim devs aren’t really trying to have small income generating items on the side which are funding the main development.
In case of airport’s a dev could create some lightweight aiports for 5 bucks on a regular basis in order to fund the development of the main product. Like a car manufacturer who is working on the next model while making money with car parts and repairs on the side.
Flight sim devs seem to jump from one main product to the next one without something than can generate predictable cash flow on a monthly basis.