Willing buyer, willing seller. You could probably buy a mansion in these countries with $500k. Someone else in the same country would take it. I'm personally happy just making enough money to be in top 10% by 30 years old, so others working remotely in the same time zone have to compete with that.

However if you're unique in a vertical, you no longer compete. Let's say you're no longer just an app developer, you're an expert in live streaming videos and CA/DRM for apps. Maybe there are regional/legal difficulties in implementing this.

Now suddenly you are worth a whole lot. A company like Netflix is willing to pay premiums like $100k for a consultant for a week maybe.

If it's a large enough niche, demand exceeds supply, and people are willing to pay closer to what they're valued.