Marketing power or proprietary restrictions?

Not sure if this was relevant for the historical cartridges but ...

Look at the .400 H&H Magnum, the .465 H&H Magnum and their introduction.

When they were introduced they were talked about all over the internet and here on NE. People here and elsewhere wanted to know about the cartridges, especially the .400. But all that was available was a several paragraph press release. Even much later they were hardly known and still the same PR paragraphs on the H&H webpage. I think that went on for years.

Eventually years later we started to see a few rifles made in the .400, as a guess a couple of mentions of people having a custom non-H&H rifle chambered for it.

I would think the actual number of rifles made by H&H in the chambering would also be quite low.

For a cartridge to become a new ".375 H&H Magnum", it would need to have real info put out to take up the interest at release time. There would have been lots of non-H&H rifles made for it, if adequate info had been available back then.

Same as Apple vs IBM type PCs years ago. IBM took over more than 95% of the PC market because multiple manufacturers could get access to the info/programs etc. Apple kept its technology for its own manufactured machines and so it lost most of the market share.

Now H&H may want all rifles made in these chamberings to all be H&H made rifles. I don't know. But the cartridges will never be popular unless more rifles and more makers have access to the specs/reamers etc. And ammo will only be available in very limited access.