I think the recent rise in the Grendel can be highly attributed to the 6.5 Creedmoor. The 6.5 Grendel received boosts in a couple of places along it's rise.
1. Finally getting the Type I & II bolts understood by the buyers and builders, the confusion caused by this slowed it's progress.
2. Alexander Arms releases it for SAAMI certification (2011)
3. Wolf producing steel cased ammo; I never understood the desire for cheap steel cased fodder for a hunting/precision rifle but it is what it is, Americans like things that go bang for cheap.
4. The rise of the 6.5 Creedmoor; the term 6.5 has accuracy, distance, easy, low recoiling, modern advancement rolled up in it's description at this point in time, and it was put there by the 6.5 Creedmoor soon after it's release in 2007; it wasn't there in 2003 when the Grendel came out. Gun people knew of the .260 Remington, and the 6.5x55; but once the 6.5 Creedmoor came on the scene everyone became "captain long range".
The nomenclature of 6.5 became a household name overnight in not just gun junkies, but in new comers to guns, and hunters who only put a box through a year. It was a BRILLIANT marketing effort by Hornady, it was a well thought out case design that overcame some minor deficiencies of the .260 REM, and the big boost came from the factory Hornady ammo that by all accounts I've heard shoots very accurate. All of this made it a sensation, a sensation that spills over into anything that starts with "6.5". If the 6.5 Grendel was called the .264 Grendel, I bet you dollars to donuts that it wouldn't have got to the level it has in the market. Not to say it wouldn't have been a success, I just think it is riding the proverbial wave of sensational marketing of a shared nomenclature.
But these are just my thoughts, and in no way takes away from the 6.5 Grendel's abilities.