Isolation. For them.
Total isolation is unrealistic for many people. Have you checked the delivery times for Amazon's grocery delivery? It takes at least 3 days to get a loaf of bread. So the at-risk folks are going to have to venture outside their homes to go grocery shopping if nothing else.
The quarantine was never about stopping the virus, it was about slowing its spread to a manageable level so our hospitals wouldn't be overwhelmed. I might add that while young people are unlikely to die from CV they are actually the majority of those hospitalized for it. I kind of prefer the scenario where I have a lower chance of being hospitalized, especially since health care is so expensive. And if our hospitals do get overloaded that will crash the economy anyway. So I will wait until someone with an actual medical degree says it is safe. I don't hire electricians to fix my plumbing and I don't let Wall Street make my health care decisions for me.
I suppose there is some amount of marginal safety for your dad keeping the rest of us isolated along with him. Is the lockdown justified by that margin?