@AngelicaKauffman To be honest, that's really not how your post came across.
But including all older people in that figure, plus those with health issues, I think we are looking at more like 40% of the population than 20%- and yes, that is still easier than isolating everyone, but you have to consider the knock on effects of that too.
Some schools won't be able to open with a combination of vulnerable people and ill people self isolating. Some workplaces won't be able to function. Some of these people are HCPs, some of them work in the care sector.
I don't think it's as simple as just saying "anyone at increased risk should self isolate".
It's also true that some otherwise young and healthy people end up needing ICU care, as well.