There aren't "hundreds of millions" of developers on this planet. The talent pool is small because just a small fraction of the workforce worldwide has the training, skills and capabilities to work as software engineers.
Sure - let's cut that number down from hundreds, to millions.
For the discussion, let's assume that the whole world of IT candidates is now your pool of potential employees. India alone seems to produce around a million computer science graduates a year. Europe, probably in the same ballpark. Rest of Asia? Who knows. Same for Central and South America. That's each and every year, new candidates that are added to the pool (minus those removed).
Even the absolute outliers would result in a sizeable number.
You are right, not all of these might have the required knowledge (if looking for experience hire), or some other number of factors.
But it would probably be easier to just start poaching top talent from top companies around the world.
