Quite simple. The ammo is still in factory packaging in basements, dresser drawers, gun cabinets, and surplus military ammo boxes all over America.
At the beginning of the last ammo shortage, I was caught flat footed. I had enough ammo for a reasonable range trip for each gun. I determined that would not happen again if I had any say so. Without insanity I was a low flame sort of heat on the last ammo fiasco. I geared up to reload, I put away a supply that with frugal use will last the rest of my career.
I was naive, I read the posts of those here and in other forums, and thought poo poo, what are they worried about. I bought an expensive lesson and the lesson was learned.
I guessing my experience is not too awful unique. When this generation gets caught up the next crises will be lesser in size and longevity. I hope... I ain't liking the frugal use proviso, nope not one bit.