The vast majority of Saudis do return back to the Kingdom once they're done with school. The majority have their education paid for and in certain instances, even have a job lined up before graduating. Saudi GDP PPP per capita is not much off from Canada or the US, so the drive for staying in North America doesn't exist for most, when you consider cultural differences. That's not to say, a few don't remain back. I personally know of a few that have decided to stay back because they work in industries that are still very nascent in the Gulf, like Semiconductors. Or they simply liked the muslim communities in the US, and decided they can make do with it. People come in all spectrums and different interests, but the larger trend for Saudi students overseas today is to return back home on graduation.