Why can't they go home for one semester?
1) It's expensive. Flight home, rent for a US apartment they no longer occupy, potential rent for a new apartment at home, flight back here next semester. Where is a student supposed to get $5000+ to deal with this?
2) They need good internet access (and a laptop) wherever they're going. Not guaranteed, and not something the university can easily provide.
3) Timezones. Many classes are synchronous and discussion-based. Not only do you need internet good enough to support video calls, but you need to be awake at the same time as 15 other people in however many timezones.
4) It might be illegal. What if you're from China or Iran and your school uses G Suite for Education? Or they use Zoom, which is banned in 6 countries. Participating in your classes would be illegal. Can the university switch their entire infrastructure to a new platform in a couple months to support a few students for one semester for arbitrary reasons?
5) It might be unsafe. Not all students have a safe and stable place to go.
6) It achieves nothing. Literally no benefit for anyone. If you expect these students to come back in a semester or two, there is no point.