[Tainnor]

1. Risk groups are not just old people, but also include a lot of people (e.g. asthmatics) that are a central part of the work force. Not all of these can WFH, they might be working in supermarkets, etc.

2. Some people don't even know they are at risk especially when they are young.

3. You can't fully isolate old people anyway. That's why we continue to see infections in hospitals, nursing homes, etc.

4. Even if you managed to isolate all risk groups, the spread of covid19 without any restrictive measures would be extremely rapid. While only a small fraction of the rest of the population would become severely ill, a tiny fraction of a large population can still be huge and might be enough to overwhelm hospitals.

If it were as easy as you suggested, surely it would have been tried - at least somewhere on the planet.