G'day Mongrel, perhaps they are not using it?
I've seen a lot of blokes who go out and buy a black-powder gun, ( talking cartridge rifles here not "front-stuffers" ), and then load them up with smokeless powder and hard-cast or jacketed bullets. I don't get it.
Had a couple of blokes turn up to one of our long range black-powder shoots with BPC rifles loaded up like that and when asked why it is always the same answer, " black-powder is too hard to clean." Nothing could be further from the truth. My rifles require at most 6 patches after a days shooting and the bore will be spotless.
Disclaimer: This of coarse depends upon the quality of the bore, your lube, bullet alloy and fit of the bullet to the bore.