In this case there has been zero marketing. The 270 has been, and continues to be an excellent "hunting" cartridge. It has NEVER, EVER, been regarded as a top target round.
Wrong.
The 6.5X55 was designed as a military cartridge to shoot 160gr RN bullets at about 45,000-50,000 PSI.
The 260 was designed to shoot 120 gr deer hunting bullets at 60,000 PSI
The long range target boys found that high BC 140-150 gr 6.5 mm bullets at around 2700-2800 fps would make darn near the ideal long range round. For a while they were taking rifles in 260 or 6.5X55 and heavily modifying them and hand loading rounds that were not in spec to shoot out of them. They were loading 6.5X55 to much higher pressures than the round was originally intended to be used at, and the longer high BC bullets could not be seated to spec inside 260 brass without taking up valuable space for powder. If the bullets were loaded out to full length the ammo wouldn't fit in the magazines or chambers. And then the barrels weren't twisted correctly for those bullets. So yes, a 6.5X55 or 260 CAN be loaded to do exactly the same thing as 6.5 CM. But the ammo is going to be outside standard specs and cannot be shot in standard factory rifles. The 6.5CM offers exactly the same performance with off the shelf rifles and ammo.
In this case Hornady didn't develop a new cartridge and push it on shooters. It was the shooters who approached Hornady and said this is what we need; make it. The 6.5 CM was the answer. Hornady has never advertised or marketed the round. It is selling by word of mouth.
And while it was designed for long range target shooting, hunters quickly found that it would do anything a 270 would do as a hunting rifle with about 1/3 less recoil. It is a great dual purpose round. There is nothing magic about it. It is simply a very good balance of light recoil, exceptional accuracy, and enough power to take anything from elk down.
And that is the thing some of the old farts can't get through their heads. Years ago almost all rifle shooters were hunters. Today virtually all rifle shooters are target shooters 1st and if they hunt at all hunting is secondary. An accurate mid weight rifle in 6.5 CM will be good enough for casual target shooting out to 1000 yards, and the same rifle with different loads will still be a very serviceable hunting rifle for any game you'd hunt with a 270. You can make a good argument that a 270 still has some minor advantages over the 6.5 CM. But the CM makes a much better hunting rifle, than a 270 used as a target rifle. The cartridge suits the needs of most of todays shooters very well.