Because many people took up buying guns and ammo who were not interested before. Also, those who have been shooting all along are all buying a bit of extra bullets, cartridges, factory ammo, reloading components, etc. so they are positive they won't run out in the middle of a reloading session.
Better to have and not need than to need and not have 'syndrome'.
Just figure, if everyone who reloads purchases one additional pound of powder and one box of 1,000 primers, suddenly there is going to be a huge dent in the powder and primer stock! Now, add to that the thousands of people who have learned from friends and family that reloading is a good sport and results in extreme accuracy, custom-made loads suited for the purpose and cartridges that are more reliable and less expensive than most factory loads!
There goes another huge "dent" in the inventory! So, in order for supply to meet and exceed demand takes ramping up of small companies and for larger companies it takes putting more people on three different shifts running the facility 24-7-365. Also figure that many of these facilities suddenly realize they must expand in order to keep up with sales. Building large additions, buying bigger, better and faster equipment all takes much time to get to the point where the business is flowing smoothly again, producing the products they produce best!
None of this happens overnight but takes time to happen. I believe a time will come when supply exceeds demand again and at that point we will all start seeing a glut in the market where they are trying to sell everything to empty all this huge inventory in warehouses and distributors!
