How?

Many Indians only work at these 30k jobs because of the possibility that they can eventually parlay those years of experience to emigrate and get a 300k job in the US. At big tech companies, many join the Indian office with the implicit or sometimes explicit promise that the company will sponsor their L1 or H1B after a couple of promotions.

I see parallels to how medical school graduates treat residencies and fellowships. If becoming a doctor meant making fellowship money forever (often 1/5th to 1/10th of what a full doctor would make), not nearly as many quality people would go into medicine.

You can only pay them so little because they see themselves as still in training for the "real job" that is in the US. Don't confuse this for true arbitrage.