RT
I believe its related to the fact that the guides want more fish landed! Alot of rookie fisherman never even know the bite happened. This double hook setup has a better chance of hook up and land for people who dont know the "bite". Its like it was said before. The long leader and the slow rod combined with the double hook gives the angler longer to feel the fish before the fish feels the angler. Thats also why they fish upstream at an angle. The boat hooks the fish and sets the hook!. Thats Boondogging! In fact many boondog boats place the most inexperienced anglers on the bow so there dragging. No skill required except to cast!
Side drifting is using the same type of gear but no angle upstream. Mostly the more experienced fisherman prefer to side drift. You feel the bite before the boat sets the hook or the fish feels you. And you get to set the hook! I prefer to sidedrift and so do alot of my experienced friends.

Thats my .02

Bob D