Availability.
Price per round.
Energy.
The 6.5 Creedmeme's sole advantage over the .308 is that, in the event that you have to make a Bob Lee Swagger shot at three quarters of a mile, it stays supersonic a little longer and shoots flatter by a single red cunt hair. There are no public ranges near me where you can shoot centerfire rifle further than 200 yards, and the closest 200 yard rifle range is over an hour's drive from where I live.
I don't hate the Creedmeme but it's the answer to a question nobody asked, just like .300 Memeout. There's no reason for either one to exist, and there's nothing they do so much better than cartridges that existed already to constitute a compelling argument for making the switch. They will soon enough join 6.8mm SPC, the Winchester Short Action Ultra Mag cartridges, the Remington Ultra Mag cartridges, .30 Super Carry, the .21 Sharps, and all the .17 rimfires on the Island of Misfit Toys with the .41 Magnum, 9x25mm Dillon, .401 Herters Power Magnum, .25 ACP, .22 Short, .357 SIG, 5mm Remington Rimfire Magnum, .30 Krag, .236 Lee Navy, .219 Zipper, .264 Winchester Magnum, 7-30 Waters, 7mm Valkyrie, 6.5mm CBJ, and many, many more "innovative" creations that nobody asked for and nobody wanted.