It's ALL marketing ploy these days.
We have had all the different cartridges and bullets needed, that's N-E-E-D-E-D, for all NA game, including DG, for about 100 years.
Speak for yourself, I guess.
Marketing ploys are nothing new. The venerated .250-3000, introduced in 1915, is one example – the desired bullet weights wouldn’t hit the desired 3000fps mark so Savage demanded lighter bullets be used – a decision based purely on marketing intentions. Marketing, which some folks hold in high disdain, is actually a necessary part of building sales – if no one knows about your better mouse trap no one will beat a path to your door to buy it.
Got my first .30-06 in 2006 and have a .30-30 and .45-70 as well, all cartridges over 100 years old. All are great cartridges which is why they are still around and popular. With the notable exceptions of the 6.5x55 (Swedish), 7x57mm and 8x57mm, most of their contemporaries have long since all but disappeared in favor of more modern cartridges.
The .257 Roberts, my favorite cartridge, has been around in its current form for quite a while but it is still a generation away from the century mark. The .22-250, is a relative newcomer, introduced as a commercial cartridge in the early 1960s and not even 50 years old, let alone 100. Ditto the 7mm Rem Mag and .300 Win Mag. My .308 Winchester uses a cartridge that is slightly older, having been introduced in 1954. Examples of all of these are in my safe. Thank you but no, there wasn’t anything available 100 years ago that I would care to have instead of these cartridges.
The flurry of modern cartridge developments has certainly introduced cartridges that, at least for the most part, duplicate the ballistics of cartridges already available, but as has been pointed out, that has been going on for well over 100 years. The raison d'ętre for these new cartridges varies and sportsmen get to vote with their wallet. Many of these cartridges have failed to gain lasting popularity while others have become very popular - which indicates to me that the free market is working as it should. Frankly, I wouldn’t want it any other way.
In the world of firearms there really isn’t much going on in the way of revolutionary new products. Evolution continues, however, and I for one welcome it. I guess we could get by with the 6mm Lee Navy, but I consider the .243 Win a better cartridge. Same deal with the .22 Savage and the .22-250, the .25 Remington and the .25-06, the 6.5x55mm vs the .260 Remington, the 7x57mm vs the 7mm-08 and .280 Remington, the .275 H&H vs the 7mm Remington Magnum, .30-40 Krag vs the .30-06, and so on. Why do I need a long tapered and belted magnum case designed for Cordite in stick form when no modern powder comes in that form? I’ll never hunt in the dry heat of Africa but I might hunt Alaska and will certainly continue to hunt elk in Colorado. Given that I’m not much of a traditionalist when it means humping extra weight around the Colorado mountains, why would I pick a heavy, cumbersome factory .375 H&H when I can choose a .375 Ruger Alaskan instead?
There were some cartridges, such as the .30 Newton, that perhaps deserved to succeed and survive but did not. Such is life. I’ll take my .300 Win Mag over the Newton anyway.
I say “Goodbye” to rimmed cartridges for bolt guns, cartridges that are too long for standard short actions and too short for standard long actions, anachronistic belts on magnums and -- with very few exceptions -- cartridges designed for black powder pressures or cordite propellants. With that said, I consider the .375 Ruger case to be the most sensible big game case to be developed since the .308 Winchester and look forward to many new cartridges developed on that case. (Yes, I know it is very similar to the Newton case.)
The only problem with firearms evolution is that sometimes its slower than I would like.