Many young people ( super spreaders) don’t show syptoms so won’t have been tested. If they don’t know they have it they’ll be out and about and passing it on before isolation is even effective surely?
Why the constant complaining about a system that’s doomed to failure?
That’s before a sizeable number of people aren’t even interested/ able to download in the app. It’s not really the governments fault if a large chunk of the population want to take their chances and just limit contacts wherever possible.