I'll just list a few of the references since I dont feel like rewriting
One overview of the primer situation 2020 covers a number of reasons including this:
"The Remington bankruptcy has had a large impact on the shortage of ammo and primers. With Remington in a state of financial insolvency for the past two years, suppliers were demanding payment upon delivery for products. Remington simply did not have the financial capabilities to have an abundance of raw materials on hand and had to shutter some of their production capacity."
quoted from Why Is There a Primer Supply Shortage? | Powder Valley
Results of the Remingon bankruptcy sale included Vista Outdoors purchase of the ammo manufacturing..
American Rifleman | The Keefe Report: An Update on Remington
November 2020 news story about restarting the Arkansas plant.
Arkansas Online: Remington buyer set to return