Because for many - especially those who live alone - spending 24/7 doing nothing but breathing in & out within the confines of four walls, for at least 3-months, probably longer, and with no visitors, is something they fear even more than death.
My Dad is in his late 80's, and following a serious heart attack last year had few pleasures left to begin with: 2 hours a week in the club, and watching sport on the telly. Both now gone. He's completely baffled by technology, so isolation means exactly that - no facebook, facetime or forums. Just him. Waking up alone, sitting alone, cooking alone, eating alone, watching tv alone, going to bed alone, and then repeat. All with a frail, slow body, that needs a multitude of pills, a hearing-aid and a walking stick to keep it going. That isn't life, its existing.
He understands the risks but also knows how much we love him, so we've come to a compromise. He will still buy his newspaper from the corner shop (a 1-minute walk) and go for a gentle walk once or twice a day. He's promised not to go to the shops, although I suspect he'll still pop into the local bakery and post office, which are on his walking route.
He knows that he must, must, must wash his hands thoroughly before and after going out, and only speak to people from a distance of at least 6ft.
He'll also still come for Sunday lunch then spend a few hours sitting on our sofa rather than his own. I won't be going out at all, other than to Dad's. Me & hubby are now using separate bedrooms & bathrooms, and sitting on separate sofa's a good few feet apart. Door handles, work surfaces etc are cleaned down at least twice daily, the downstairs loo is thoroughly cleaned after every use, and we now use paper towels instead of hand-towels.
Should Dad still be unfortunate enough to catch this awful virus, at least his final weeks & months won't have been in isolated misery. He won't want saving, he's made that clear.