The average age on this forum is like 60+. They did a poll a while back, I might be a little wrong, but it is an older group of people, for sure.
As a younger guy, it's much "cooler" to go deck out your AR that will never be used for anything other than photos, or get the newest, latest, space age material pocket rocket gun.
Muzzleloading just isn't trendy anymore. Everybody I know who muzzle loads does it solely for the purpose of extending hunting season. They have no actual interest in the sport. They get a modern inline and all they are interested in is hitting a deer or whatever. They could care less about types and grains of powders, and weights of bullets, as long as it hits what it's supposed to, and those modern inlines do make it really easy. I was invited on a BP only hunt, and bought everything I needed at Walmart. Pretty much all of it was made by the same company. (I then became interested in old fashioned muzzleloading, so don't knock the guys who buy modern stuff, without the introduction, I wouldn't be here)
Anyway, where I'm going with this, is that machine shops and fabricators have a much larger market in custom parts for modern weapons, or "easy" BP stuff. Old fashioned muzzleloading is an old man sport, and we are no longer what the manufacturers are looking for. It's turning into an "extended hunting season" sport, and nothing else. Other than these forums, and my neighbor who ML's to extend his hunting season, I've never even met anyone interested in the sport (that I know of).
There's some awesome guys out there making beautiful muzzleloaders, but think about what's more lucrative, making custom, decked out, video game weapons for gen Z for their Bitcoin money using C&C machines, or a hand designing a beautiful rifle, that could take literally hundreds of hours to complete?
I would bet that in 20 years, finding people who make custom muzzleloaders will be almost impossible, and everything will be made by only a few companies, sold at big box stores.