We don't shut down the road network despite the number of deaths that causes.
How many lives would a lockdown really save? And how many years of life will it save? If it kills people now that would die of Flu next winter that is different than if it kills someone in their 20s. Nobody really knows the answer. How many road deaths will be saved due to lockdown? How many extra deaths from heart failure due to people not exercising? How many fewer deaths from people not eating junk food?
How much is the economic cost of that lockdown? Again nobody really knows - without a lockdown people are still likely going to be more subdued in their economic activity from a social point of view.
One thing that is sure is that healthcare systems will collapse without a lockdown. How many lives do hospitals save each year?