Why does not the lift produced by main wings create pitch moment?
Of course it creates a pitching moment! Now we need to define around which reference point this moment should be measured.

If the reference point is the center of gravity, it is even equally strong as the pitching moment of the elevator, it only has the opposite direction.

If you use the aerodynamic center as the reference point, the moment will be less strong. If the wing airfoil is symmetric, the moment will actually be zero (ideally), but with a cambered airfoil there is still a measurable moment left.

A moment is always a combination of a force and a lever arm, measured perpendicular to the direction of the force. Only when the lever arm is zero will the moment disappear. If we use the center of gravity as the reference point, the weight will have no lever arm and will contribute no moment, but the distance between the wing's lift and the center of gravity is large, so this moment is large, too.