Many people don't understand why 6.5 Creedmoor became as popular as it did, or why it's a better long range cartridge than 260 to most shooters.
It's easy to convert a 308 to 6.5 Creedmoor. That made it trivial for manufacturers to offer a 6.5 Creedmoor if they already offered a 308, or for shooters to convert a 308 to 6.5 Creedmoor. You can use the same bolt and magazines without issue. It's easy for a cartridge to get a foothold when many shooters and manufacturers just needed to swap a barrel to use it.
Compared to 260 Remington, 6.5 Creedmoor is better suited for long, high BC bullets in a short action rifle. That gives it an advantage over 260 Remington for long range shooting. Factory twist rates play in here too. While that's not an issue for people shooting custome rifles, the majority of shooters use off the shelf rifles from the local gun shop.
6.5x47 Lapua has the same advantages as 6.5 Creedmoor and was released around the same time, but never really caught on in the US. The two are more or less the same. Had 6.5 Lapua been introduced by a US company it probably would have taken off instead. We're no better or worse off with Creedmoor than we would have been with Lapua.
6.5 Swede, 6.5-06, and many of the other cartridges that provide ballistics similar to 6.5 Creedmoor need a long action. That eliminates the possibility of converting a 308 to 6.5. There's some disadvantages to long actions, especially in the competition settings where Creedmoor first took off.
6.5 Creedmoor is intended to be a long range cartridge that fits within a pretty strict set of constraints. It's popular because it's one of the best performing long range cartridges that fits the constraints it was designed around. I've never seen someone who actually shoots a 6.5 Creedmoor make the claims the haters go on about. It's a slight improvement over the 308 that does a little better at long range, and the people who actually shoot it are aware of that.