Headhunter explains why tech jobs are going overseas

The United States has lost 28% of its jobs in high tech since its peak in 2000, claims a study released recently by the National Science Board. This means 687,000 positions have been lost. Why has this happened?
I’ve lived near Silicon Valley for three decades. I’ve always regarded the high-tech hub as a permanent dynamo in the USA economy, an employment source for it’s citizens, and ground zero for the future’s scientific breakthroughs. Imagine my surprise when I queried a “headhunter” recently who informed me that times-are-a’-changing; high-tech is migrating to Asia, and why be surprised?