article from 2006, Cardinal José Saraiva Martins, then the prefect of the Congregation for Sainthood Causes, gave Pope St. John Paul II's reasons for canonizing so many saints:
The first reason the Pope gave was that he, by beatifying so many Servants of God, did no more than implement the Second Vatican Council, which vigorously reaffirmed that holiness is the essential note of the Church; that the Church is holy: one, holy, catholic, apostolic.
John Paul II also said that if the Church of Christ is not holy, it isn't the Church of Christ, the true Church of Christ, the one he desired and founded to continue his mission throughout the centuries.
Therefore, John Paul II said, holiness is what is most important in the Church, according to the Second Vatican Council. Then no one should be surprised by the fact that the Pope wished to propose so many models of holiness to Christians, to the People of God.
The second reason is the extraordinary ecumenical importance of holiness.
In "Novo Millennio Ineunte," the Pope said that the holiness of the saints, blessed and martyrs is perhaps the most convincing ecumenism, these are his words, because holiness, he said with even stronger words, has its ultimate foundation in Christ, in whom the Church is not divided.
Therefore, the ecumenism we all want calls for many saints, so that the convincing ecumenism of holiness is placed in the candelabrum of the holiness of the Church.
The Pope's third reason was that "the saints and blessed manifest the charity of a local Church," that is, today, the Holy Father said, local Churches are far more numerous than in the last 10 centuries.
Therefore, we shouldn't be surprised that there are also more saints, more blessed who express and manifest the holiness of these increased local Churches.
The Vatican website has a list of all the saints he canonized and the Bunsons (Matthew and Margaret) wrote a book about those saints, published in 2007.