First, every shooter isn't necessarily a hunter. I know a number of them.

I can't count the numbers of hunters using muzzleloaders, that were totally scared to death, to take a shot beyond 40yds. Even with their modern inline. They had the thought, or it was instilled into them, that muzzleloaders were only close range rifles. Modern inlines are not just 40 or 100yd rifles.
Second, not everyone who hunts with a muzzleloader or any firearm for that matter, has the ability to "hunt". The terrain you hunt can be completely different than what they can hunt. Eastern/southern hunters may have more woods and brush, where short shots are the norm. Mid west hunters may have a single hedge row to hide in, over looking an 80 acre bean field. Western hunters may have vast areas, miles of wide open, hills, or mountains. Shots at game vary by geographical area. So lumping all muzzleloader hunters into a "no reason" to shoot long range is far from correct.

I do though like your last paragraph. Its spot on. That is exactly why any shrink wrapped rifle is capable of 300yds or 300m accurately. Shooters just have to learn from someone how to properly utilize the rifles they already have. Its no secret, it just has to be learned.