It's about the math. The number of cases requiring hospital care Vs. the number of ICU and hospital beds available. This will vary from nation to nation.
The US has 34 ICU beds per 100,000 of the population, the UK has 6.
What the politicians fear is bodies piling up in the streets, so isolation will continue to avoid that spectacle until resources match demand.
Things will reopen in a few weeks because it's impossible to lock up an entire nation for months but you're likely to see spikes and probably rolling lock-downs for a few more months, probably on a regional basis determined by trends indicating a probable outbreak in particular hotspots for which protocols will be put in place.
Expect mass gatherings and big events to be cancelled till the end of summer.
Expect a very slow reopening of select businesses. A bookshop is low risk, a bar however is not.
Everything will be done to 'manage' the burn so there will be a lot of ad-hoc plans and rules put in place until a vaccine starts getting rolled out.
One think I know that Jaws has taught me.
The beaches will be open for the 4th of July!