When 6.5CM passes the walmart test (it has btw), you know a significant number of rifles have been sold.
The firearms market always has that unique combination of innovation, propaganda, and sales figures. Like anybody else, manufacturers desire to sell high markup items. Product lines have their cycles. They get old and need to be refreshed. A new rifle in a heavily promoted caliber? - check. Premium ammo in that hot caliber? - check. A spokesperson to attest that this is the best ever? - check. Manufacturers always want someone to have a reason to purchase another firearm, new ammo, or components no matter how minute that performance difference may be.
New rifle calibers, precision rifle matches, and the current long range fad have given life to the (I'm using this loosely now) "hunting rifle" sector that has been stagnant for years. Maybe now it's dressed up with picatinny rails, a polymer stock or chassis and has "tactical," "precision," "stealth," or some specific name other than some letters and numbers - it doesn't matter, it made the sale. Maybe the person buying it can't shoot it to the equipment's full potential. Maybe 80% of the "long range rifles" sold are never used past 400 yards. Maybe the barrels chambered in long, skinny bullet calibers do have a shorter maximum life than 30 caliber. Maybe these specialty long range hunting bullets/cartridges aren't ideal at all when "Cody" ("Bubba" is too old and too busy butchering Mausers - haha) shoots his deer at whopping 40 yards this fall.
I hate to put it in this light, but I doubt the manufacturers cared about any of those maybe statements as long as people bought new guns and new ammo.
It really is a buyer beware market in terms of rifle calibers. Being an early adopter and chasing the hot caliber can bite some consumers. As we know, calibers aren't usually gone for good, but they can get really expensive. We have seen some WSSM's, RCM's, and specialty AR cartridges become incredibly hard to find or at a cost that is just prohibitive. I can still remember hearing the salesman's spiel about the 325 WSM being the best ever.
There have been advances in bullet technology, coatings for powder technology, stagnant primer technology (environmental, I suppose), but I feel that manufacturers are literally "throwing designs out and seeing what sticks" when it comes to brass. At the end of the day, it's easier to promote and sell something new than it is to excite people about a legacy caliber or product. On top of that, they do not necessarily cater to the performance minded or analytical minds of most THR'ers. Manufacturers want "Cody" and others to think they can live the dream of having the kinds of rifle skills portrayed in video games if they just purchase the right products.