Because people in red zones have decided not to value the elderly. Yet older people have more wealth and may want to trade it for health.
So they'll try to get out of red zones.
research.stlouisfed.org/publications/e…
No one over 50 wants to get COVID-19. It's the angel of death for them. So it's rational for them to get out.
If you can't, then you're exposing older folks in your region to serious risk. They may protect themselves by leaving.