What is the mythological background behind Gaya becoming a Pind Daan Tirtha?

According to the Gaya Mahatmya and Padma Purana, Gaya is named after Gayasura, a powerful demon who performed such intense penance that he earned blessings making his body so pure that anyone touching it would attain moksha. The Devas, unable to manage the flow of liberated souls, requested Lord Vishnu to intervene. Lord Vishnu, in a divine act, pressed Gayasura into the earth with His lotus foot, creating the sacred imprint now worshipped at Vishnupad Mandir. Gayasura requested that Gaya become a place where people could offer Pind Daan to liberate their ancestors. Lord Vishnu granted this boon, thus sanctifying Gaya as the most sacred Pitru Kshetra.