Lot of funny and complicated answers on a straight forward question..
Lowering collective reduces AoA, and in forward flight this reduces flapping and make the rotordisc tilt forward, this will cause the liftvector to tilt forward and anybody who been awake on the lesson where the helicopters stability has been the subject, will understand why the fuselage tilts forward.. Stabilizers and precession and those factors are not the main contributor in this matter.
Fly safe
