well this is where all the modelling comes into play. if the health services aren't stretched at all, and you lock everything down, sure, you stopped the risk of them being overwhelmed. but what then? just stay locked down forever? at some point you then have to ease off the restrictions - and with that the same risk will be back (hence the 'second wave'), which takes us straight back to the beginning again.
the UK's numbers saw that without restrictions, the health services would be overwhelmed. so lockdown was the right thing to do. you can't just assume that's also the case for every other country in the world. every country is different, and it's a given we can't stay locked down forever. when you start and finish each lockdown (and there may be more of these, I'm sure) has to be based on the modelling. if Sweden think their numbers show that its health services won't be overwhelmed (and they are modelling into the future), then it makes no sense to lockdown too early.