One reason is because of primers. Primers are simple to make, but cost prohibitive to get into making. They are made with explosives, so all sorts of permitting, licensing, facility requirements, etc is very expensive. For the most part, bullet manufacturers rely on just a handful of the larger companies to produce primers. If they themselves were to make primers, it would take to long to become profitable, so most just opt to buy. The shortage will eventually ease up, so I don't think any company wants to take the risk of making a small profit now to get into primers, just so they see that investment sink them later. The demand exceeded the manufacturing rate by several fold, and ate up what little reserves there were. Now the companies that make primers are making bullets as fast as the primers are coming out, leaving non to be sold. That is why the smaller bullet manufacturers are not producing anything right now.