Lu, you asked for an explanation in my own words and I will attempt it, in non engineering terms.
If I lift up on a rotor blade that has a delta hinge, the pitch changes, correct?
Take a helicopter and let's use a Bell 206
with conventional rotorhead...
Place the rotors in the lateral position.
Move the stick back and , naturally, the advancing blade has positive pitch of 5 deg. approx.
Now go and walk the advancing blade around over the nose. Precession tells us that the blade will be highest here and pitch =zero.
Lift the blade UP because thats where it would be with back stick.
The rotor is tilted back , the blades have zero pitch and the stick is back. All is well.
Now, lets leave it in that position, but REPLACE the teeter hinge with a delta hinge.
Now look at the blade in front. It is raised up, so the delta hinge will pull pitch out and the pitch will be less than zero.
Can you see that that delta hinge is up to no good?
It is pulling pitch out of the blade when the swashplate wants the pitch to be zero.
The pitch actually was zero at some point before the blades got to the fore and aft position.
The only way to get the pitch to be zero in the front is to phase the pitch links like a R-22.
That's it. That's the best I can do.
Forget the dissymetry of lift, that is a minor point compared to this