They believe that there are basically two mitigation strategies. One is to have a very drastic early lockdown that shuts down the virus before it spreads widely. The problem with that is, once you lift the lockdown it will simply start all over again. The problem with this is lockdowns are most effective the first time you do them, and then mostly in the first few weeks of the lockdown. Do it too early, and yes it will be very effective in the short term, but later on when cases become much more prevalent the lockdowns will be less effective.
The option they are going for is to start the lockdown a little later in the cycle. The hope is this will make the lockdown more effective at a higher point in the spread. Effectively instead of a series of booms and busts, you get one longer slower initial burn and then you’re mostly done. They believe that in the long term this will make it easier to protect those most vulnerable to the virus, because you only have to do it once, at the cost of increased prevalence among people least vulnerable to it. So they see it as a better longer term strategy.