It's a combination of a lot of things:
1. More people recovering and infection rates slowing.
2. Expanded testing for diagnosis and antibody testing
3. Identify effective existing or fast tracked treatments. See all the quick and dirty clinical trials.
4. Expand hospital capacity (beds, vents, ppe, staff)
5. Masks for the public
6. Recommendations for ongoing social distancing (group size, number of customers, etc.)
7. Recommendations and processes to keep at risk people at home as much as possible.
All of things are needed to adequately manage ongoing infections until we have heard immunity or a vaccine. Most of us probably need to get infected but we need to be able to prevent and care for anyone that gets severe disease. There's no way we go back to "normal" for a long time. Otherwise, we end up back where we started and every large city looking like NYC and NO. The 15 day thing was never going to be just days.