Also, it might not be actually possible -- or at least be quite risky for the student. Whenever you enter the US, border agents have almost unlimited authority as to whether you are allowed in, especially as a student. Speaking as someone who's spent years going through this process, every time you have to enter the states, even if all your paperwork is in order and there are zero rational reasons for you to be denied entry, you're still worried about it. Some border agents are friendly and let you through quickly, and some grill you like you're trying to forcefully invade their country. I had a friend (who was on a work visa, not even a student one) who taught English as a Second Language at a US high school, who was told by a border agent that she's lucky he's letting her through this time, because they shouldn't allow foreigners to teach English at American schools.

That's not to even mention that when you're on an F-1 student visa, you can legally renew it while remaining in the US even while the visa stamp in your passport has already expired. But once you leave the US, you have to have a valid visa stamp in your passport in order to reenter, even if you already have a valid F-1 visa document approved and signed by all the right people. This means that, in your home country, you'll need to make an appointment, spend hours lining up at the US embassy (if they're even open due to COVID), then go through the interview process (which you have to repeat every single time you renew your passport visa stamp) in order to get that stamp reissued.

Once, after already having spent years in the US on a student visa, I was actually turned back during that interview because the particular consular officer on duty that day decided that I needed to provide a detailed printed transcript of my American high school experience. I had to leave the interview, schedule a second appointment, and have the printed transcript ready at that time. All of this is to say that not only would requiring students to go through this process simply because their universities aren't offering physical classes during COVID will not only cause intense stress, but also will probably result in some students not making it back into the country for arbitrary reasons.