If it were called a .264, .260, or 26 Grendel then nobody but enthusiasts would even know it exists. I'm not talking bad about the cartridge at all, I made my choice between the two and am sure I wouldn't have regretted choosing the other one bit. But let's face it, cartridges like these, including the 300blackout and other AR compatible non-5.56 rounds, are typically utilized by a much smaller portion of the shooting world. With the marketing campaign the Creedmore has seen if you put 6.5 in front of anything and it's going to be an eye catcher.
Didn't the 6.5MM Grendel come before the CM?
OP, I have both and to me, the Grendel is more appealing. It can do what the 6.8 does at short range but leaves it behind at long range. I still love my 6.8 and use it exclusively for hog disposal. As you pointed out, ammo for both is scarce.