Why Is US Grad School Mainly Non-US Students?

I am a new graduate student in Computer Engineering. I would like to get my MS and possibly my Ph.D. I have learned that 90% of my department is from India and many others are from China. All the students come here to study and there are only 7 US citizens in the engineering program this year. Why is that? I have heard that many of the smarter Americans go into medicine or the law and that is why there are so few Americans in engineering. Is this true?