Why is St. Pius X called the pope of frequent communion?

Answer 1

He changed the order of the Sacraments of Initiation from Baptism-Confirmation-Eucharist to allow people to receive communion before they were confirmed (which then was usually about age 14-16). He allowed communion to be received as young as 7.

Catholic AnswerPope St. Pius X, of happy memory, attempted to undo the Jansenist influence in which people were barely ever receiving Holy Communion. One of the problems, with which he did not deal was the Communion fast was from midnight the night before, this was a problem for many people, especially those who could only attend a later Mass in the morning. It wasn't until the reign of Pius XII that the communion fast was lowered to three hours. But St. Pius certainly did more than any other pope in centuries (up until that time) to overcome the scrupulosity of many to return them to Holy Communion. Now, of course, we have the opposite problem, everyone going to Holy Communion, and few going to Confession. And yet, to receive Holy Communion in a state of sin is a grave sacrilege.

from Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980

Frequent Communion. The practice, dating from the first centuries of the Church, of receiving Holy Communion often, as a means of growing in union with God. Weekly reception was customary already in apostolic times. From the end of the second century many priests and laity received every day. By the thirteenth century the practice has so declined that the Fourth Lateran Council had to legislate at least annual Communion at Easter time. In the sixteenth century the Council of Trent urged the reception of Holy Communion at every Mass attended. During the centuries of Jansenist influence, Communion became rare, until 1905 when St. Pius X decreed that "Frequent and daily Communion, as a thing most earnestly desired by Christ our Lord and by the Catholic Church should be open to all the faithful" (Denzinger 3375-83). The only conditions required were the state of grace and the right intention.