There’s been lots of interest here in grad school articles recently, especially where it is a relatively bad deal or career decision. They’re all related somehow, but I think this is probably more about immigrant/native dynamics than anything else.
In the late 80s, my Mum did a PHD in the US and we lived there for 5 years. Many of her friends were foreign grad students. Others, Texan academics.
Migration via academia has always been a good option. There are special visas. Sometimes financial support. A foreign students application form. More importantly, there’s a structured and welcoming subculture you join by default. You will have a place in university society.
I’m reminded of a provocative (to me) Tyler Cowen bit about formal dress and class mobility. When culture (corporate culture in that case) is formalised, it is easier for outsider to adopt and participate in. You can buy a good suit. You can’t easily adopt ways of speaking, casual fashion, and such. They’re too subtle for outsiders. Cultural signals are still important, but the subtle ones are more exclusive because they are subtle.
Anyway, something similar is probably happening here. Academia is formal. It’s meritocracy is formalised. You can talk funny and think funny, but you’re still a PHD candidate, professor or whatnot. You can access that “social capital” to put it in annoying modern terms.
Like tyoma suggests in this thread, natives have more options to choose from.
There are other reasons, of course. I suspect this is one of the top ones.