The virtue of the .264 and .257 Magnums are they shoot flat. When most hunters were using MPBR, that flatness significantly increased range. With most hunters using laser range finders, and BDC reticles or custom BDC turrets, is that little extra bit of flatness worth it? The cost is high recoil and faster throat erosion and therefore shorter barrel life. Lower recoil alone would probably result in more hits and when the rifle gets shot more often in practice that increases even more.
Here's the other thing. Those belted Magnums are flatter than something like Creedmoor, but they're not longer range. There are two things about the Magnums that conspire against using the kind of extreme low drag bullets that give Creedmoor and PRC cartridges their reach. The first is twist rate. Most of the Magnums have 1:9, whereas the very long ELD bullets need 1:8 or less to stabilize. The other thing is the location of the case neck in relation to the overall length. The Creedmoor and PRC are set back to allow for a very long ogive. The Magnums would exceed the magazine and receiver length if the same bullets were seated. Remember those "Magnums" were actually not .375 H&H Magnum action length. They were shortened H&H Magnum cases. They were shortened enough to fit into a standard-length receiver. They're not designed to hold very long bullets, but instead, they hold a lot of powder for small bullets.
Of the belted magnums, the .300 has its place in long-range because it's been established there for some time. But it's been outclassed in LRP shooting by the 300 and 6.5 PRC and other cartridges. The belted magnums could still be a good choice for hunting, but here is why I think not. It's clear because of their big-powder load, shorter-bullet design, the magnums (the belted magnums like 257 Wby, .264 Win, and 7mm Rem) are going to shoot flat and hit hard in normal hunting ranges (out to 300 yards). Now factor in light-weight, monolithic copper bullets (because who wants to eat meat splattered with lead at over 3000 fps?). The copper monos (TSX, TTSX, GMX, E-Tips) will stay together at high velocity, but they are usually lighter weight for the maximum length allowed by the neck position, magazine length, receiver length, and twist rate. So unless you are shooting game at 300 yards or more, they will strike the meat at about 3000 fps. At a more common 100 yard range, a shot could destroy a lot more meat than a more sensible non-magnum.
So basically these belted magnums trade-off practically everything for flatness out to 300 yards. They have:
higher recoil
use more powder
faster throat erosion
shorter barrel life
more meat destroyed at most common hunting distances
shorter range than low-drag LRP cartridges
and they require a standard (long) action receiver whereas other cartridges offer greater performance out of a shorter action
Here's one more thing: With good bullet selection, nobody could tell the difference between the belted magnums like the .264 WM and 7mm RM and a good ol' .270 Win. You have to look hard at the ballistics charts to see any difference, and in the real world, it's just not there.
FWIW, I do not have a rifle chambered in Creedmoor, PRC, or 270. I am not a "fan-boy." I am a regular American that has to win the lottery before I can shoot one deer. I don't need a Magnum or a 1000 yard rifle to shoot a little deer on the rare occasion I win the lottery. I'd really rather get the opportunity to hunt game with my children, and they don't need a Magnum or a 1000 yard rifle either. I apply for an Elk tag every year so someday I can have what will probably be a once in a lifetime chance to fill a bull Elk tag. But if that chance comes, it's going to cost me that entire year's time off work to fill the tag (which means zero for my family), not to mention the expense of having the quarters packed out and processed. What I'm saying is, don't expect enthusiasm (and sales) for something that most rifle owners will never do anything with and really have no use for.