Why is Pratipada Shradh specifically for maternal grandparents?

The Dharmasindhu and Nirnayasindhu specify Pratipada as the tithi dedicated to maternal ancestors (Nana-Nani). The reason is rooted in the Vedic understanding that the maternal lineage holds a distinct spiritual relationship with the family — mothers are considered a primary source of nurturing, and their parents by extension deserve special, dedicated honour. Pratipada, as the first day of Pitrupaksha, is given this responsibility.