F-1 (student) visas are already nonimmigration visas. After you graduate, you have a few months of "optional practical training" (OPT) and then you're expected to go home. Hopefully, you can get an H-1 (another nonimmigration visa) to stay for at most six years, which is about how long it takes to get a Green Card (permanent residency)[+].
I had heard that the reason why F-1s are nonimmigration is because back in the 1960s it was seen as foreign aid with Cold War benefits. Encourage people from third world counties to come to the United States, see how great it is, and then go back and build up their own countries. A decade or two out, you now have a country friendly to US interests.
Maybe that made sense in the 1960s, but it seems like it stopped making sense sometime in the 1980s, and certainly by the 90s.
We make it too hard to immigrate to the US. If I was king for the day, I'd make F-1 visas immigration visas, or at least be able to fast track F-1s into an immigration visa. The glacial pace, and the difficulty to immigrate is a reason why people go back. I know people that ended up giving up on getting Green Card, so moved to Toronto, and already has gotten Canadian permanent residency.
[+] If you want to fast track your Green Card, marry a US citizen. You get it in a couple of months.