The higher nose angle on approach is due to the leading edge slats or droop.
The wing angle of incidence is designed to give minimum fuselage drag in cruise.
Changing the wing camber only using trailing edge flaps gives a "flat" fuselage incidence on approach - a la Fokker 100 (and light aircraft).
Adding a leading edge high lift device in effect reduces the incidence of the wing in relation to the fuselage.
Therefore the fuselage needs to be pitched up to have the wing at the optimum AoA on approach.