While I'm not an expert in the small arms ammunition industry, I think there are four major factors to the shortages we're seeing in the USA.

First, there are a lot more first-time firearms owners in the USA than in any usually 6+ month term that I can think of.

Second (and closely related to the first), many firearms owners have more concern about public safety than they've had in the past.

Third, there are concerns about potential future legal restrictions.

Fourth, I'm told that there are shortages regarding specific components, especially primers, related to the pandemic. I don't have any data to support that, but it seems plausible.

As for me, I've been training more this year than in any other year, as I had planned long before any of the above factors came to light.

The two calibers I train with are in short supply everywhere, and when available they're priced much higher than a year ago. But they are possible to find, with some effort.