This is so foreign to me, living in Europe.
The salary here is in my experience based on where the company is located. Big city, big salary.
Perhaps the company doesn't see it worthwhile to argue over peanuts.
Btw, it's getting bigger in the US as well over the least few decades.
Singapore is a place with a smaller gap, and less regulation. That's part of the reason they went from third world to first world.
Where you put your developers shouldn't make much of a difference to how much business you have?
However you are up to something: big cities tend to be more productive. That's the reason people and businesses put up with the higher rents and other inconveniences. See https://en.wikipedia.org/wiki/Economies_of_agglomeration