So is it strictly the rifles that make the difference? What if you used Tikka rifles and match ammo? I believe the CTR or the T3x comes in both cartridges.
You're largely being mislead. None of the Creedmoor's popularity has anything to do with rifle availability or ammo.
The 30tc was a niche round, a solution for a very specific problem. It did not and does not match .30-06 performance, and barely hangs with .308win performance, when loaded to similar pressure. There's no replacement for displacement - the .30-06 is a considerably larger case, and picks up about 200fps over the .30tc or more when equivalently loaded in similar barrel length. So against its class mates, the 30tc had no advantage.
In the second, the creedmoor rounds have far less recoil than the 30cal Thompson Center round. While the 6.5 and 6mm creedmoor cartridges are both no more than niche rounds too, their niche is considerably more popular right now than was that of the .30tc, and in their application, low recoil is king. Generations prior had predominantly bought rifles for hunting, where impact momentum is far more critical than it is for steel games. The modern market is much more focused on recreational plinking than hunting, so 30 cal recoil is largely unnecessary, so guys don't buy heavy hitters any more. When I was growing up, middle aged shooters would say you needed a 7mm mag for 1,000yrd shooting (old timers would say you didn't need to shoot 1,000yrds). Today, guys are reaching out farther with short action non-magnums than most guys were with belted mags 30yrs ago. The big difference, in my view, is we were focused on killing something upon arrival back then, and less so now.
Thirdly, the 6.5 and 6mm rounds beat the 30 cals for trajectory management. When guys play UKD games, or KD games of variant distance, trajectory management is a huge issue. A guy can get a 115 Dtac with a BC of .588 running about 300fps faster - and therefore considerably flatter - than the .30TC can push a 150grn bullet with a low to mid .4 BC. When running multiple targets back and forth out from 300 to 1200yrds in the same stage, that gap means a lot.
In the Fourth, the market supports them. How many factory rifles have you ever seen in .30TC? How many boxes of factory ammo did you ever see on a local shop shelf? Fantastic cartridges will die if they aren't marketed well. It's en vogue right now for guys to thumb their nose and say the Creedmoors are only popular because of marketing, but it's not really truthful to say that. Alternatively, it is VERY true to say, "if you build it, they might come, but if you don't build it, they damned sure won't." I'm not sure any cartridge has hit the market with as much manufacturing support as the 6.5 creedmoor. Guys aren't stuck with limited availability, low quality brass, we're not stuck with only a model or two of rifles from which to choose, we're not stuck special ordering rifles or ammo. It's all on the shelf. Unlike many of the other "big hype" cartridge launches in the last 30yrs or so, the creedmoors hit with great timing, and fantastic support. Good product, good placement, good timing - that adds up to good sales performance.
Finally - I mentioned performance of the .30tc against its classmates above, but I've held that discussion for the 6 and 6.5 creedmoors until this point. When the .30tc hit its niche, there were already three powerhouse cartridges dominating the 30cal market, or even 4, with a great number of other players on the field. The .30-30, 308win, .30-06, and .300wm were already standing tall above the other dozen or so cartridges with more limited popularity. The .30br, .300rum, 300h&h, 300savage, later the wsm, x54, and a gaggle of other cartridges flood the 30cal market. The 6.5creed really only had the .260rem with any popularity in the 6.5 market, there just weren't many players in its class, and the 6mm really only had the 243win to deal with. The 6.5 A-Square, 6.5-284, and x55 swede are too long for short action rifles, and run more powder, meaning less barrel life. The 7-08 is often weighed against the 6.5, but it has the same issues the 260 suffers, and it runs out of mag room AND powder capacity below the high BC, heavy weight 7mm bullets. All of the 308 family cases suffer the mag length issue - however trivial it might be, and the fact there simply weren't many others in the game left the door wide open for a short action, steep shouldered 6.5.
The fact luddites don't care for the 6 & 6.5, favoring the older cartridges somewhat like them, does not change the fact they are incredibly effective, incredibly popular, and incredibly well supported rounds.