[jessriedel]

> there isn't any exit border control

There is, but it's done electronically by monitoring passenger records. It's very difficult to exit the US without creating a paper trail, which is vacuum up, so the DHS definitely has info (albeit noisy) when aliens don't leave.

https://www.quora.com/Why-does-the-US-not-have-immigration-c...

One reason not to interview people when they are leaving is philosophical, or slippery slope, depending on your political persuasion. Exit restrictions are obviously very disturbing, being classic precursors to fascism/dictatorships, and generally immoral. (Yes, there are cases where people commit crimes or otherwise shirk duties and the state has a justification for preventing their departure, but these are relatively rare.)