Same reason .223 is less expensive then .222 magnum. They are almost the same cartridge size wise, but there is 100x more .223 sold. Maybe 1000x more.
Exactly, a production line can run .223 for 360 days a year and have each days production shipped on the same day to distributors, no storage or inventory costs.
That same line gets retooled and runs .222 for 5 days and it takes the manufacturer a whole year to sell that 5 days worth of production, incurring storage and inventory costs to do so. Those costs get passed along in the final ammo price.
Add onto that the fact that the manufacturer needs to be compensated for taking the time and effort to retool that line for .222 ammo and then back to .223. If they only made 10% profit on both .223 and .222 then they wouldn't even bother making ANY .222, they would just keep the line cranking out .223 year round. However if they charge a 25% profit on the .222 then it makes sense for them to take the line off of .223 production and make as much .222 ammo as they can sell. Sure the .222 ammo will be more expensive, but at least you can buy all you want.
So you have the additional storage and inventory costs PLUS the extra profit required to motivate the manufacturer to endure the inconvenience of retooling a line for a low-volume cartridge. Nothing evil or exploitative about it, it's simple economics.
If you want the cheapest price on a certain cartridge then the volume needs to be high enough that a manufacturer can run a production line in that cartridge for close to 24/7/365. The longer that a manufacturer can run a production line without having to retool the cheaper the price will be.
This is why it was impossible to get 380 ammo during the 08 shortage, with demand so high for 9mm no manufacturer was going to take a production line down to retool for 380, the resulting 380 ammo would demand an even higher premium that most people wouldn't pay.