Here is an article putting together data from GitHub about SW developers per country.
https://data-player.com/highest-number-of-software-developer...
When talking about outsourcing jobs from the U.S., you’re obviously gonna exclude the U.S. China is also not a factor. Neither are Western European countries or countries like Japan and S Korea because of relatively high salaries. Russia is out due to long standing geopolitical issues.
That basically leaves Brazil and Indonesia as the only alternatives to India in the top 10 and combined they don’t even have half the number of SW developers as India.
You need to then add Mexico, Vietnam, Turkey, Philippines and Poland to the above 3 to add up to the number of SW developers present in India.
Thats why the outsourcing industry is concentrated in India. You can setup 1 office in India and have access to as many SW developers (Indians are also very willing to migrate domestically, so an office in a single city is sufficient to cater to the entire domestic developer market) as you would if you setup 8 offices in & different countries across 4 continents.