I always had the idea that the aircraft designers had a design cruise speed with the wing around 3º AoA, then tried to build all the other bits pointing directly into the wind for minimum drag
Maybe it was due to rising fuel costs at the time leading to adopting a slower, more economical design cruise speed.
Changing the wing/fuselage angle on later versions would be a major item, but re-alighning the engines would be fairly easy.