Most disposable PPE is made from certain types of man-made blown fabric. For a variety of reasons, the production of this fabric is concentrated in China. It's not a terribly environmentally friendly process and China was willing to make it without regulating it to death.
The production of the PPE articles eventually concentrated close to the source of the fabric production (China) to save shipping costs and enable just in time production.
Sterilization, where required, is also a chemically-dependent process that most people don't want in their back yard. China was also more flexible on this and lots of sterilization started being done in China.
PPE is a Class I medical device regulated by the FDA. You can only produce these products in a plant that is FDA approved to make that specific product. The time to stand up a new PPE manufacturing facility is 18-24 months.
China's COVID outbreak led to the shutdown of most of their factories, which meant not only were companies not making PPE, China also was not making the necessary fabric to make them from. Even if you had a FDA-approved facility with capacity to make PPE, you can't get the raw materials on a large scale.
And all this is on top of pandemic-related factors like hoarding, increased use, and thin hospital inventories.