There's some concepts being assumed that don't always stack up for new gun buyers at a retail long gun store.
First, 6.8 has been out for so long that many of the bulk ammo shooters are not buying retail off the store shelf. That business went to the internet as soon as vendors could offer the deals. And the same will happen to .300BO - why buy ammo for $17-25 a box of 20 when crates of 500 run well under a dollar a round - close enough for some to just buy new brass rather than spend a bunch of time cutting down old milsurp?
Second, not all the buyers of a new caliber are reloaders. The impulse gun purchaser looking for a New! gun is doing it more for the novelty than a long term commitment. It's a status symbol. In the case of the 6.8 we started seeing the boutique shoppers falling off about four years ago as other cartridges crowded the market. The Caliber of the Month club is currently focused on .300BO, it still remains to be seen what happens when the next New! cartridge is introduced.
This goes to the AR remaining popular - which it will - but buyers are fickle and the generation coming up, the 14-20 year olds now, may have a completely different idea of what they want in firearms. They grew up with the surge in AR's, who knows what gun will be their generations example of something different they can hang their ego on.
Not to forget that there has been a strong tradition for inch designations in the civilian gun market in America. A new cartridge will more likely be named in that system than metric. Instead of naming it the 6.8SPC, Remington could have gone for .277 SOCOM. Marketing has a lot to do with it.
You know how the game is played, which would catch your interest at first mention, a .277 SOCOM, or 7.62x45 Whisper? Young buyers don't know or generally have a good grasp of ballistics - hence the current trend in 18-22" 6.8 hunting rifles. They want their gun to be just a little better than everyone else's and they will go to an extreme to do it.
That's where shelf supply is an important factor. The 6.8SPC II loadings aren't readily seen on the shelf, but .300BO is perceived as being the hot rodded 5.56 round that is bigger better than the other guys.
Marketing and perception play on the buyer's notions. It's all a game of plucking the strings of the heart and having the product sing the siren song of male enhancement.
It's why you see so many 3/4 ton Diesel pickups purchased just to get one guy to work as a commuter vehicle. "I have a Diesel truck, I shoot a bigger bullet, I am better than you."
When that mindset is questioned, it's not just numbers or using it in it's best operating parameters, it's questioning the very maleness of the owner. Exactly why we have four pages of monkey dancing as various fanboys attempt to jockey their position on the subject to prove they are not so much Right, but Superior in the male pecking order.
Again, it's where we are in the current market cycle on the .300BO. It's a comparison to 6.8, and as a very telling point, the last year, most conversations have been .300BO vs 6.8SPC. And the barely mentioned other cartridge isn't given much shrift. It has it's run, and the sales are simply falling off as new shooters don't read about it anymore. 6.8 moved into the international military market, and .300BO? Never made it as a 3Gun cartridge back 30 years ago. It doesn't have a good history, it's just a wildcat reborn for short range and suppressed use.
If my gun can shoot further than your gun with a flatter trajectory, then I am better than you. That statement has been treated like fact for over 70 years in the industry, so seeing .300BO play off it's short range use is bucking the trend.
Dedicated fans of a caliber will reload brass to their hearts content - that is not an indicator of anything when there are so few new shooters taking up reloading. It's an advanced activity for older guys 25 up, and certainly much less an impulsive buy at a LGS by the newly graduated into manhood. What those guys want is the better cartridge over a 5.56, and that is what sells in the long run. The .300BO is far from disappearing from the scene, but lets see what competition brings out at the SHOT shows the next two years. I suspect the ammo and gun makers would very much like to get people away from easy reloading into a cartridge they need to buy off the shelf where they play on their field.
Expect a lot of hype and comparisons why that New! cartridge is better than .300BO. They will ignore 6.8 because it would be a tough sell.