Can't speak specificially to the Airbus but general comments -
It is forward CG so there is speed increment in Vapp to create higher aerodynamic forces for better handling
While the higher speed may well be associated with better control responses, I suggest this is not the consideration behind the speed increment.
One consequence of CG is that a more forward CG generally is associated with a higher stall speed than is the case at more aft CG - routine fact of life in the design and certification world.
A lot of performance numbers are based on stall speed - and, in this situation, V1 and Vref/Vapp are important to field length, for instance.
It follows that an OEM has the choice of a simpler AFM using the most critical (highest) stall speed or, at the OEM's choice, a more complex certification with multiple stall speeds based on CG.
If the vast bulk of operations are going to be aft of x% MAC, then that MAC is probably a better option for run of the mill stall speeds. For the less usual circumstance of a more forward CG, the appropriate higher stall speed is used and this is seen by the pilot as an AFM requirement to add a knot or two to the speed schedules.
why we need MAC ZFW?
Standard weight control requirement. Correct load is figured for BRW/TO and ZFW to cover the possible range of CG in flight associated with FBO.