Firstly, that’s not what you wanted of him, see above. Secondly, on what basis would he encourage people to make their own? N95 masks are a special construction and I’ve seen no indication that anyone had any reason to believe that a homemade version wouldn’t act like a power diffuser for pestilence.
As it is, the common t-shirt sleeve mask and nylon sock mask are both more dangerous to the world than going bare faced. I asked on this forum a decade ago about the science of masks, because I was living in Japan at the time, and the answer then was that an N95 mask becomes more harmful than helpful after 30 minutes of use because it soaks up germs for about 30 minutes and then reaches its threshold for absorption and/or threshold for keeping a hang on the little guys and then you start creating plooms of aerosolized germs every time you exhale through the diffuser that you’ve just created.
To be clear, homemade masks, made in accordance with now-known guidelines and used appropriately (removing from your face when away from other people and washing/changing regularly) are useful in stopping the spread of Covid. Masks made inappropriately and used incorrectly vary between useless to harmful. There is no law of the universe, so far as we were aware in Spring of 2020, that it was feasible and useful to make effective masks at home. Outside of N95, you may as well have gone around licking the walls so far as any other type of mask was concerned.
20/20 hindsight doesn’t change the knowledge that we had in the past. George Washington’s doctor didn’t lie when he said, “I can help you, sir!” That doctor proceeded on to kill the first President, but he had a genuine belief in the medical knowledge of the day and that’s just what it was at the time.