why is there a sudden drop of binding energy around low mass in nuclear binding energy?

Answer 1

If by 'low mass' you refer to the periodic table of elements and the actual masses of the Elements themselves then the reasoning would be that there are fewer extra Neutrons in the Lower weights.

While transiting upwards along the mass weights of the atoms in the periodic table of elements, the number of Neutrons to Protons begins to climb in such a manner as there now becomes More unpaired Neutrons in the nucleus of the atom, the changing binding 'point' is occuring as a result of the phenomenon.

The Neutron being the 'gravitational particle' makes it The 'Binder'.

Otherwise, (Not refering to 'low mass' that way) I know nothing.