Because he had to to help us all in the long run. There was a shortage. The administration EARLY on, also foolishly sent to China, tons of our own protection gear and masks, without thought of our own shortages and needs to come.
All states were scrambling to get enough masks for our own medical front line workers, who were already having to use their mask on hand for up to 5 days, before changing it out, when protocol requires them to change it, after each patient visit. We were even begging carpenters and plumbers and any businesses that had any masks, to please consider giving them to the hospitals. Doctors were using their own money to find any masks they could from our own pharmacies, hardware stores, even eBay.
In China, the day they told their people the truth about the new virus, Jan 10th, all surgical masks were sold out, in every store carrying them and every pharmacy, in less than 1 day.... ALL OF CHINESE Stores sold out. There was an article in the news on this January 11th, from multiple media outlets....
They could not risk the same thing happening here....
In addition, there was no scientific studies done yet on this specific virus...determining how it was spread, airborne or by touch....No tests how long it survived in the air or surfaces of various sorts, no tests done yet on how long it stayed in the air, or how far it can reach if coughing etc etc etc.
After a month or two, throughout the world, scientists were running experiments and tested those things, and got their actual answers for this specific New virus...