I did a little bit of a dive into the current ammo shortage.
The root cause seems to be a lack of primers. Part of this is due to manufacturing shutdowns and part of it is due to the primer manufacturers set up to produce to average demand. Between the downturn in production and the upturn in demand, there simply aren’t enough primers in the pipeline and no spare production capacity to catch up. I’ve read upwords of 90% of available primers from the four domestic primer manufacturers (IIRC, Remington, Winchester, CCI and Federal) are going to ammo manufacturers but it’s a trickle compared to normal supply and there’s practically nothing left for reloaders.
Apparently, and I don’t know how true this is, there were plenty of primers overseas and many are on their way via ship (see https://www.gunsandammo.com/editorial/great-primer-shortage-2020/383204). There are several primer manufactures outside the U.S. including Fiocchi, Armscor, JSC and Sellier & Bellot.
Anecdotally, I’ve found that not only are primers fairly impossible to obtain (especially large rifle), but the little Lee Loader kits are unavailable in certain calibers (30-30 is the one I was looking for essentially without success).
Also, due to copper shortages, it’s very difficult to find copper-clad 22lr ammo although lead versions are not too bad.
I picked a heckuva time to try to get into reloading for the first time...
SGAmmo.com : Due to extremely high demand and very limited supply we are very short on inventory at this time....
Seems about right ... My stores were stocked DEC 2019!... I saw the writing on the wall coming out of China... this is enviable