Their economy can't afford the hit. With the affects of Brexit and the uncertainty a post Brexit Britain they can't afford it. They can't close everything down, with a massive hit to their economy.
America and china can weather the storm. They literally just invested 1.5 trillion into their stock exchange which is half our annual GDP because of it struggling.
They'll have to shut down everything soon. Even if they don't nobody will be leaving their homes when the number of cases peak.