There's a big difference between what constitutes a "succesful" cartridge from one perspective versus the next. As a consumer, I look at a cartridge that has been popular for a century, and from my perspective that makes it a success. But a ballistics nerd looks at a "new" cartridge and sees minute "improvements" in certain facets of its performance, compared to the old favourites, and says "Wow! Look at that BC, look at that sectional density, look at those improved energy figures, more, faster, shinier...that's a success!"
A gunmaker introduces the new 6.7Cringemore, markets the crap out of it to those guys, and sells a trainload of rifles. That's good, in the short term...but to keep selling to that second group, they need a more newer, more faster, more shinier followup a few years later. That way, the nerds need to buy another rifle because the "old" one...that they bought 3 years earlier...is now just obsolete trash. To a gunmaker, a gun that has built-in obsolescence, and necessitates the purchase of yet another gun shortly after, and then another, etc...that is the ultimate success!