Why are there more foreign students? I believe it was Amy Chua that wrote the article about Tiger Moms, and, unsurprisingly enough, the demographics break down similarly for piano students. IMO it's that foreign students are more driven to be robots in hard things (piano, engineering, etc...). Of course, this also does come with some insidious downsides:
A) they do exactly as trained. Aka they're human robots. They can do what you teach them perfectly--but truly come up with brilliant, independent, creative ideas? Not so much.
B) If the pressure gets high enough, they just break down. I remember in my IE 447 class at Lehigh, after the second exam, the professor gave us the chance to redo the whole damn thing open book because one girl just completely broke down. I just wanted a nap after the exam.
C) Language barrier. I don't care how smart you are with math. Ever tried to listen to an overseas student communicate? I'm not sure when I'm going to be in a position to hire, but from what I've heard speaking with these people, I'd rather hire an American who's finished the same program with worse grades than an overseas student with a massive language barrier in the way.
Now...another fact as to why there are more of them?
Because China has 5x the population of the US.
Think about it. Now that some of them have the $ to pursue an MFE, they want riches, so they go for that kind of thing.
Also, I'm not sure that so many American people actually want these kinds of quant jobs. Hell...I remember one of my high school classmates...blew me out of the water in math and physics (was one of the smartest people I've ever met at the time), beautiful as all hell, got into Columbia for a BS in Financial Engineering, and even managed to intern for an investment bank. Twice.
Unfortunately, the investment bank was Lehman Brothers, and when Wall Street went up in smoke, she went on the actuarial track, pricing life insurance policies (or so it seems from her LinkedIn).
And this girl was one of the brightest people in high school, period. Missed her at the 5 year reunion due to what I hypothesize to be a family tragedy, and, well...
One person (of Chinese descent) was pursuing a PhD in theoretical physics at MIT. I was the only one with a completed quantitative graduate degree. A couple of people got investment banking/other non-math financial industry positions, one person who pursued the same program as the aforementioned young woman and then went onto get an MFE at Columbia is now an assistant trader at SIG. Oh, there's one more who's working as an IE for the Navy, and I'm really happy for him.
Overall though, I don't think that Americans like math though. Period.
And the grad schools are making it hard to even pursue a graduate education in anything quantitative. Duke (PhD stats), UPenn (PhD biostats), and UMich (PhD Stats and PhD OR, two separate programs) all rejected me, and my credentials aren't horrid. 770 Q GREs, 3.81 MS Stats GPA...and nope...I got shafted. (Though two of my recommendations arrived late at UMich)...heck, even my own alma mater, Lehigh, rejected me after I applied to my old department for a PhD when I got my first 4.0 at Rutgers, and SUNY Stony Brook took me for a PhD in quant finance--but with no funding.
Frankly, I think a lot of this could be solved if US citizens were prioritized in PhD programs over foreign nationals. Given how few Americans actually like math or engineering, this may actually be a sensible course of policy to get our country back on track.