It is most likely a secondary effect. New gun sales are skyrocketing, and when people buy new guns they typically buy ammunition for the new gun.
Then people are hoarding ammunition in fear of not being able to obtain ammo as you have described and also in fear the price will go up.
There has been some limited discussion of taxing ammunition as an element of gun control.
Reloading supplies are also taking a hit. Go to the "Powder Valley" web site and notice the out of stock status of small pistol primers and the limited supply of some popular powders. You can get the small one lb. containers but not the more economical 8 lb. containers of powders.