Why was internal wiring not an option?
The thickness of the cables (4 guage) would have made them bulky and evident under the carpet. These cars aren't made with the sort of cavaties that modern/bigger cars are, so there's no way to get stuff behind door trim, etc. Plus, when the carpet is down, that's pretty much down for good, 'cos it's glued (fits better - no movement).
I guess we could have run cables under the carpet along the transmission tunnel usually, but the V8 exhaust runs up by there and it gets very hot! Also, this way it's a pretty easy job to run extra cables or repair stuff - just jack up the car and feed the new stuff through. The result? Everything looks stealth. The kickpanel speaker grills have been resprayed to match the leather (light stone beige), so they're pretty much invisible - or at least no one can see they're Hex's. (We found a company that makes spray paint to cover plastic/vinyl that matches your leather - you send them a sample and they make you a few cans. It's been a god send around the dash area!)
Bet you're sorry you asked! ; )