Cause, as much as messing with percussion caps, black powder and lead ball ammo...plus the great fun cleaning up the gun after only about a couple dozen shots fired.
And mind you....all that IS great fun..
Just loading .38 Long Colt rounds into it really is less trouble all around.
Just call me lazy...
But when you have three or five people wanting to shoot the gun.....DANG, my way is easier.