A few facts.
Winchester, the leading US ammunition and case manufacturer by far until recently, has never made either brass or ammunition for the 260 Rem. I'd suggest that tells you a lot.
AFAIK, Remington has never loaded a single match round for the 260 for general sale. It has treated it entirely as a light/medium deer round. Remington Arms has likewise offered it in a very limited choice of rifle models with the sole exception of the immediate early 1980s post-launch period. When it didn't become an immediate big seller, Remington appeared to largely lose interest in it. Without the arrival of the Remington model 7 lightweight / short alternative to the 700, I doubt if the 260 would have survived at all. Not that many other manufacturers, rifle or ammunition, picked up on the 260. It was left to specialist 'boutique' ammunition companies to load match variants of the cartridge.
Remington either failed to notice the advent of 'practical' and sniper matches in the US 20 odd years ago where the 260 and its AI variant were the dominant cartridges, or if it did notice couldn't be bothered to capitalise on it at all.
The 260 as
@jcampbellsmith points out was never well suited to heavier / longer bullets as long as it's loaded for short actions / magazines. The trend in the 21st century is towards ever heavier / higher BC bullets, hence longer.
6.5X47 Lapua is a specialist cartridge, which like 6BR is heavily weighted to custom rifles and handloading. No US manufacturer was ever going to pick it up. In fact how many European rifle manufacturers did? I found two, just two rifle manufacturers with barely any model choice, and I suspect rarely had any in stock to sell. plus Blaser which offered a barrel in the chambering for a while.
6.5X55 will never become big in the US mainstream manufacturing area - long action; SAAMI restricted loadings because of Krag and Swedish Mauser pressure limitations; a foreign military number.
6.5 Creedmoor was designed as an affordable match cartridge for people who don't handload from day one. It is very well designed for the US market and its stated purposes. Hornady didn't even launch it with any varmint or deer loadings - that came later due to shooter demand. What Hornady did do from a year or more before day one was get other manufacturers on board - Savage, Ruger and Howa; GAP and others in the custom tactical field; PT&G and other reamer manufacturers. The ammo was in the dealers and there was a good choice of new rifles launched simultaneously in time for day one, with review examples for US shooting journalists, and the big gun shows like SHOT (which also sees 'range day' testing / trying-out opportunities out in the nearby desert for accredited journos).
Marketing spend? I doubt if Hornady spent as much as Remington or Winchester did on equivalent cartridges. Anybody who shouts 'marketing' implying it's a way of getting customers to adopt a poor product knows nothing about the subject - there are examples by the bucket-load of crap products, or that addressed markets that didn't actually exist, that failed miserably despite massive marketing and PR spends. Hornady did the whole job - design, listening to and working with those out in the field who know their business through and through, getting enough product into local gunshops and the big US chains and suppliers - really well. Remember, the 'Creedmoor' bit of the name is partly an iconic name from US target shooting history of the later 19th/early 20th centuries, but is also the name of a very much 21st century successful US shooting business (Creedmoor Sports) and it was a partnership between individuals in the two outfits which came up with the concept based on knowing the US match shooting scene intimately.
Hornady did have a HUGE stroke of luck though. Their collaboration with Sturm-Ruger just when the latter was designing and putting the Ruger Precision Rifle into production tapped into the about to be biggest growing/selling range segment of 'blackticool' rifles and PRS. It was a win-win for the two companies - Hornady got a day one entry into the scene and Ruger got a very efficient new cartridge as a USP for its new model. We in the UK were way behind at this stage. I spoke to the Viking Arms people as to what the UK sales RPR cartridge breakdown was at the Northern Shooting Show a year or two after the rifle's launch. Overwhelmingly 308 Win, a few 6.5s and you can hardly give 243s aways they said. I bet a lot of 308 RPR buyers kick themselves now - there are some very good secondhand buys there today. Within 18 months every Western rifle manufacturer was looking to rush a PRS type chassis rifle into production and not a single one doesn't offer 6.5 (and mostly now 6mm too) Creedmoor as a chambering option.
