Why not?
@SkipdiverJohn's position is not an unpopular one. It's also a difficult one to balance. Is it better to be cautious and protect those most as risk, but at the same time create more risk of mental health issues, isolation, and damage to the economy (thus driving people out of jobs, causing further mental health issues, poverty etc), or is it better to protect those most at risk, but tip the seesaw the other way. The original solution of the government paying everyone to stay at home isn't sustainable as soon the government will run out of money. It's only a short term patch.
We have to have economic activity, people need to go back to work etc in order for the country to function and in order to have government money for the less well off. If money stops going into the system, the system will collapse. There is an argument to say that many people shielding would be shielding from *something* even if Covid19 wasn't around.
So then we look at the middle ground. Is there a position where we can reduce the spread of infection but have people working, and doing the things they usually do? That's where we are now. Some things just can't work, or just don't work. Arguably, Pubs don't work as they are high risk for infection spread. Things can be done in summer months such as table service outside for example, but the more people you have inside, and the more drunk they get, the more likely they will spread infection.
Planes are problematic as they enclose air in the cabin for long periods of time. Theatres are problematic as they tend to only be viable to very full houses. More testing will help, better and more effective treatment will help, but there isn't a quick solution. So we are in a place where Covid whackamole is probably the best solution.