This has two answers that become one.
Its a political and social economic class battle going on. For one thing who uses black powder?
SImple really, the everyday guy using a 400 dollar gun from cabelas. While the people who make the politics are at the highest economic strata of society.
These are the people who feels its necessary to have a 4000 shotgun for each type of hunting they do (one for upland, one for downland, one for shooting ducks off a jon boat, etc).
This group has been turning hunting into a rich man only sport. Theyve made it a "requirement" to spend 4000 to buy a deer, and then spend 5000 for a week at a gamefarm/hotel/entertainment complex to shoot at deer over a feed station.
And then look at modern weapons, they brainwash people into thinking its worthless unless you opt for the 2000 wonder scope to go along with the 1200 rifle..... And then the ammunition, unless you want poor performance from your new rifle, you need to reload or purchase high performance ammo. And that puts you on government lists, sad but true that buying even 1,000 of .22 short puts you on a list for being a "survivalist" which they call a "terrorist sympathizer or anarchist".
And then like here in Michigan, bout 20 years ago the state cops started trying to get black powder guns banned. Seems that bullet proof vests dont work with crap when hit with roundball from a pistol or even a brownbess. And to get rid of those you get rid of the good propellent, black powder.