Online lectures in a lot of uni's will still happen in real time. Meaning that some students have to take classes at 3 AM. Being in the same time zone will still make a difference for a lot of them.
1. Not every foreign student can afford a "paradise" on a Caribbean island
2. Not every foreign student has fast, stable internet and reliable electricity for online classes
3. Most of the world doesn't enjoy the free passport access US citizens have to the rest of the world.