The thing is that, in the normal run of things, government doesn't procure PPE. The users of PPE procure it.
Now, to take stuff like gowns;
Gowns have (believe it or not), a very short shelf life. I believe it is 6 months, That makes keeping a stockpile somewhat tricky,
Let's say that you keep a stock of gowns that is enough for 4 months normal use, and that you employ stock rotation. That means that you are continually trying to sell gowns that are short shelf-life, and nobody wants to pay full price, so you continually lose money on the stockpile.
Worse than that, the 4 month stockpile, which is about as much as you can keep without just throwing stuff away is for normal use. If you suddenly need 4 times as many gowns, your stockpile exhausts in a month.
When something bad happens there is never a shortage of people who have 20/20 hindsight on what should have been bought,