Because until the number of vaccinated people in the community reaches acceptable levels, the risk of spreading the virus to the unvaccinated remains high.
But what's an a acceptable number? As the age brackets decrease the number of people we need to vaccinate increases. So we're going to bankrupt the country while we wait for everyone to be vaccinated from a virus that probably isn't going to kill anyone under 20? Honestly enough is enough. If you are that scared of this you take personal responsibility and stay home. Meanwhile I would like to get back to work and alot of businesses and the majority of the population would like to get on with life.
We need to stop being scared of all these ridiculous scenarios that may or may not eventuate and just get on with life. Even if we spent more on some covid hospitals response it will still be better than burning the entire country to the ground economically. If this is still going like it is in 12 months noone is going to care about covid as the economic reality is going to hit and hit hard. Airlines will go bankrupt. People forced to sell houses lose careers and savings. You cannot shut down economies for 3 years it just doesn't work. The country has had 2+ years to prepare. That is enough.