In my line of work, there are actually a bunch of Vietnamese guys making Western level quant trader type salaries, living in small castles in their home country.
The thing is, you can't suppress the wages unilaterally for someone who knows how to do things. There's always going to be some other firm offering them a similar deal, with the same capital (equipment, IP, support, trading capital etc) for them to use. So even if you know they only need a tenth of what a Western quant needs to live well, you can't just offer them that, they will end up taking an offer very similar to what they'd get if they moved to NYC or London.
The $300 people are victims of supply and demand. Often it's cookie-cutter type contract work that many people know how to do, and the real problem they have as a supplier of that knowledge is how to get in the front of the queue to be the guy to help a western small-time entrepreneur build his website. When this is the case, the organiser, basically the owner of the outsourcing company, has all the negotiating leverage and sets the price accordingly.
The difference is that the firm with very specifically exploitable capital needs specific knowledge to operate that capital. You need devs with certain skills, and there's only so many of them, especially as your process gives a lot of false negatives. As such devs are rarely identified, you are wasting a lot of money not splitting the pie generously when you find one. I was talking to someone the other day and the agent told me there were 40 candidates interviewed for three roles, which is a huge amount as I had 5 one-on-ones plus a takehome.
Firms that don't really have anything special will not pay anything special, in relation to where the employee is based.