It doesn't work like that. Look at cyberspace right now. Israel, Iran, North Korea, Russia, China, all hacking the out of the US left and right.
In the company I work for (F100) our top employees both are and come from all over the world... Netherlands, Germany, Japan, Brazil, France, the UK... heck, I came to the US on a H1B visa (citizen now).
And there's also the factor you mention, a lot of these people retire early and move on to do other things, start up their own companies, and then they need experienced people.
What you're talking about indians is the consulting firm stuff I was mentioning, which is a scam. That's literally a scam, it's well known and neither this or the previous administration have cracked down on it, and the sole purpose is to drag down salaries on the code monkey jobs. It's more prevalent outside of silicon valley, though.
It also completely breaks the purpose of H1B visas, which is to bring exceptional talent.