Convenience and easy to clean. I am pretty sure the invention of bp wasn't a walk in the park either. At my local there's almost next to none who still use bp as many have converted to either Pyrodex or Triple7 and still shooting great scores. I tried bp a couple of times and the mess it creates and the time it takes to clean up was better spent with Tiple7. Everyone has their preference and at least the ones I shoot with, black powder is much lower on the list compared to Pyrodex or Triple7. I have never felt either of these powders unsafe to handle and use much less volume of Triple7 to achieve what I want compared to my trial of bp.
Yes you use less 777 by weight, than black. The conversion factor is 77.7% Pyrodex is something similar.
So a 454g tub of 777 (£52.60 from Kranks) is equivalent to 584g of black. I.e. £90/kilo equivalent.
Whereas Kranks sell their own brand black for £51.60/kilo
Or Zloty Stok for £65.10/kilo
Or the very best Swiss stuff for £82/kilo.
I must admit that I've only ever used Swiss.
https://www.henrykrank.com/muzzle-loading/black-powder-caps/black-powder.html
I agree that the substitutes are safe to handle, and store without the need for a wooden box. But that's where it ends as far as I'm concerned. Hmm, a more expensive substitute vs. the real stuff ?
BTW Swiss powder is IME much cleaner burning than Pyrodex. Shooting a 30" barelled .45 calibre rifle, sidelock, no. 11 cap, even when the Pyrodex didn't hangfire or worse, the barrel needed swabbing after no more than three shots before the tight patched (.451 swaged lead) round ball couldn't be fully seated. Even pounding on a steel ramrod. Nightmare. End of shooting. Unscrew the breech time, than bash it back out again. Had to swab after every shot. Whereas with Swiss I could keep on going for at least five shots before thinking about swabbing.
Something different about the residue. That from black seems to soften up with traditional bullet or patch lubes. Pyrodex doesn't.