bellydeep,
I don't have any inside info, but that's what happens with cartridges that don't turn out to be all that popular: The ammo company starts trimming back factory loads to those that sell most, but make even less of those, because it doesn't make economic sense to manufacture a bunch of ammo that isn't going to sell. And when ammo doesn't sell, retailers don't order it.
Which is one reason the .300 Winchester magnum is by far the most popular .300 magnum, and probably always will be. There are millions of rifles in .300 Winchester Magnum already out there, so there's always a market for ammo. You'll find .300 Winchester ammo in any store where big game ammunition is sold, whether in Montana, Alaska or Africa. (The other reasons are it works well, even though it's not quite as powerful as some other .300's, and the case fits and functions in any "long" bolt-action, even those only long enough for the .30-06. And non-loonies don't care if it has a "useless" belt or short neck.)
One older gun writer always moaned about the lack of a variety of factory loads in less-popular cartridges, saying if the factories only offered more loads, then rifles for the cartridge would be more popular. But as noted, that's backwards: The lack of variety in factory loads is due to rifles in that round not selling well, minimizing demand for ammo.
Once a cartridge becomes a "standard," however, sales tend to keep rolling or even increase, because just about every rifle manufacturer chambers the round. Which is why just about every rifle manufacturer and ammo maker offers the .223 Remington, .22-250 Remington, .243 Winchester, .270 Winchester, 7mm Remington Magnum, .308 Winchester, .30-06 and .300 Winchester Magnum. Those are the biggies, partly because they all fit and function in just about any bolt-action made without any problems. (Some other cartridges are on the fringe of standard, including the .25-06 Remington, 7mm-08 Remington, .300 WSM and .338 Winchester Magnum, so get chambered frequently but not consistently.)
It's hard for any new cartridge to crack that line-up, because the standards and semi-standards work for 99% of hunting anywhere on earth. While rifle loonies can (and do) argue that their particular favorite is "better" than an old standard, the differences are so minor (especially for the average hunters and shooters who buy the vast majority of factory rifles) that they're meaningless in the field.
Factories keep trying new rounds, though, in the hopes that they'll become the new standards. At the very least they'll sell some new rifles to loonies, and once in a while they win the lottery. Since 1950 Remington won with the .223, .22-250 and 7mm Magnum, and Winchester with the .243, .308 and .300 Magnum.
It will be interesting to see if ANY 6.5mm round ever cracks the list of standards, but the slots a real winner can fill are pretty narrow anymore, which means there are a bunch of has-been and wannabe cartridges. And in a high-demand market like today's, manufacturers aren't going to produce ammo and brass for those rounds like they do for the standards--and in fact they might even be relieved if some of the non-standards disappeared.
