I guess the reason "why?" is nice to know, and it may only be "that's how we did it. sure it could have been on the inside, but we put it on the outside".
Whatever, either you follow the Boeing repair, completely, or you make your own repair and substantiate it.
Btw, if you're doing your own repair, copying someone else's and saying your one is "equivalent" is a bit of a cheat ... since you don't have the analysis supporting the copied design, and some airworthiness folks won't buy it.
another day in paradise, or is paradise one day closer ?