It depends a lot on what you're hiring developers for. If you need a developer to add some new UI features to a web app, there will be thousands of junior developers you can hire. On the other hand, if you need to reduce the time it takes to execute a stock trade by 0.25 microseconds, there may many fewer developers in the world with the domain knowledge (high frequency trading) and programming skills (high performance C++ programming) to do that. Even fewer developers will have the skills needed to write the flight control software for a new spacecraft.