The hard evidence is that the mass manufacturers of bullets are busy marketing the other calibers, preferentially over the two calibers you're interested in. Opinions may talk more than money, but sales and profit drive business decisions. The decisions that determine business success or failure.
If you were the one making and selling the bullets, would you prioritize manufacture of bullets in calibers used by ~5% of customers, or in calibers used by 50% of your potential purchasers? If you choose 5%, that explains why you're not making bullets for a living. You might try to address that 5% of the customer pool after you'd completely addressed (oversupplied) the 95% of the market. But even then most likely only in the most popular bullet weights in those calibers - initially.
Most manufacturers want to maximize the odds for success. In doing so, their business decisions rely on something more than if we build it, they will come. Something more than a field of dreams. Hammer Bullets is no different. They have to focus on business success, initially. They are unique in that the tool up costs for production of odd caliber bullets is much less with their manufacturing process compared to most other bullet manufacturers. Otherwise they wouldn't be offering the oddball bullet calibers at business startup.
