"Why is cowboy action shooting in with Black Powder instead of being included in Competitive Shooting?"
If I remember correctly, I'm actually partially responsible for that.
Years and years ago we didn't have a Cowboy Action board.
With the growing popularity of the sport, though, the owner, Rich Lucibella, decided to add one, but he wasn't sure whether he wanted to add a stand alone forum, or whether he wanted to pair it.
I (and possibly others) suggested pairing it with the Black Powder forum for a number of reasons:
1. The Cowboy Action genre seeks to recreate or emulate activities that mainly took part in the black powder era.
2. The BP forum is a general forum, discussion all aspects BP, including rifles, shotguns, handguns, etc. That also fits in with Cowboy Action shooting, in which rifles, shotguns, and handguns are used.
3. Many Cowboy Action shooters load, at least in part, black powder for added authenticity.
4. And, personally, I wanted those stinky charcoal burners out of my Revolver forum.
There you have it.