Why was the day of Ashura specifically associated with Moses (peace be upon him), to the exclusion of Muhammad and Jesus (peace be upon them)?

Fasting on the Day of Ashura is a Prophetic Sunnah (tradition). The reason for it is that when the Prophet, peace and blessings be upon him, arrived in Medina, he found the Jews fasting on that day. They said it was the day Allah saved Moses and the Children of Israel from Pharaoh, so Moses fasted it in gratitude to Allah. The Prophet, peace and blessings be upon him, said: "We are more worthy of Moses than you," and commanded its fasting. When the fasting of Ramadan became obligatory, the fasting of Ashura became a Sunnah and not an obligation.