The virus is different to what we initially thought it was. More deadly and less contagious. 'Flattening the curve' is the strategy for a virus which can't be stopped by distancing, which results in good immunity for people who've had it, and for which there is effective medical treatment. You're aiming to slow it down so that everyone can get the treatment, then be immune. Covid CAN be stopped relatively easily through social distancing and doesn't have very effective treatments, and we're still unsure how long immunity lasts after infection, so 'flattening the curve' is the wrong approach.

New Zealand started on a 'flatten the curve' strategy, then responded to new information, changed course, and eliminate the virus. They still haven't seen a resurgence. It took 4 weeks of hard lockdown.