Why did the Church say that an entrance hymn (like the Protestants have) is better than a Gregorian introitus nowadays?
The Church has said no such thing.
In fact Gregorian Chant is still the official chat (music) within the Roman (Latin) Rite.
On 22 November 1903 by Pope Pius X issued a motu proprio Inter pastoralis officii sollicitudines that detailed regulations for the performance of music in the Roman Catholic Church. The title is taken from the opening phrase of the document. It begins: "Among the concerns of the pastoral office, ... a leading one is without question that of maintaining and promoting the decorum of the House of God in which the august mysteries of religion are celebrated...." The regulations pointed toward more traditional music and critiqued the turn toward modern, orchestral productions at Mass.
It also made Gregorian Chant the official chat of the Roman Rite.
For Pope St. Pius X, the greatest gift the Church possessed to reestablish all things in Christ was her liturgy, in particular, the Mass. If the Church could purify her liturgy from the influence of secularism and inspire a more faithful appreciation and love for the Eucharist, Catholics would have the supernatural grace and strength to withstand the assaults of the modern world. It is for this reason that his first motu proprio (a papal letter addressed to the entire Church), was Tra le solicitudini, arguably the most influential papal document on sacred music ever written.
Throughout his entire priesthood, Pope St. Pius X made liturgical renewal one of his central goals. As a young boy, Giuseppe Sarto was intimately involved in Church music, singing at Sunday Mass and even forming a new choir at his home parish. In the seminary, his command of the church’s chant was so exceptional that he was placed in charge of all seminarian chant. In his first parish pastor assignment, he established a school of chant for both children and adults, where he experimented with various styles of chant.
In addition, during the early years of his priesthood, Fr. Sarto encountered the Benedictine monks of Solesmes, a community founded by Dom Gueranger with the mission to catechize the faithful through the signs and symbols of the liturgy. Fr. Sarto’s relationship with the monks of Solesmes helped him reclaim the ancient tradition of Gregorian chant at the local parish level. He found the Church’s most ancient tradition of Gregorian chant to be the easiest for people to learn and the most effective at drawing them more deeply into the mysteries of the faith.
The Benedictine Abbey of Solesmes was asked to preserve the sacred treasure of Gregorian Chant.
As such they has endeavoured to publish a new Missal in the Ordinary Form of the Mass of Pope St. Paul VI with all the Propers of the Mass in Latin and set to Gregorian Chant, published in 2012.
The new Gregorian Missal, printed by Solesmes in 2012, is truly thrilling. I’ve never seen a book with nicer printing of the chant: crisp, clear, beautiful.
That being said, I do have a few minor questions about the Foreword. Let me review some items, then I will ask my question. For anyone not aware, Solesmes has gone through the entire book and replaced the old (discredited) ICEL translation with the 2011 (more accurate) translation, as required by Church law, but they could not do this for the Mass Propers, since no official translation exists. However, there does exist an official translation of the Spoken Propers (i.e. Introit and Communion antiphons). Therefore, Solesmes carefully went through, replacing the Introits and Communions in any instances where the Spoken Propers correspond to the Sung Propers.
Another way to put this would be: the Mass Propers in this new publication correspond to the (previous) Solesmes translation, with the exception of any Introit/Communion antiphons which match the Spoken Propers. In those instances, they have substituted the new (2011) translations. - Gregorian Missal With The New Translation!
Unfortunately nowadays, so few priests and lay persons desire to preserve their liturgical heritage and thus vernacular hymns have now become so commonplace in parishes. This is however what Rome wants to avoid. The Mass in the vernacular has indeed damaged the sacred traditions of the mass and the will of Rome.
The reception of this motu proprio throughout the world has a simple, but also complicated history. It is simple in that it was mostly ignored throughout the universal church. However, it is complicated in that it was ignored for a variety of reasons, depending on the musical culture of particular regions. In the United States, there were two dominant trends within liturgical music that help explain why it wasn’t well received.
First, the Irish Catholic immigrants to the United States in the 19th century brought with them very little customary practices concerning liturgical music. The Irish Catholics experienced great persecution for their faith in their home land and often had to celebrate Mass in secret without music. One could argue that silence was their liturgical inheritance. Thus, for Irish Catholics in the United States, there was very little participation when it came to singing the Mass.
Second, the German Catholic Churches were greatly influenced by the Protestant Reformation, which eliminated chant and replaced it with modern hymns. Thus, many German Catholics in the United States were more accustomed to singing cultural or national hymns at Mass rather than chanting the Mass.
Overall, the general attitude of American Catholics in response to Tra le solicitudini was that of apathy or indifference. The majority of American Catholics of the early 20th century preferred to have hired singers rather than embrace a new culture of the lay faithful singing the parts of the Mass. Chant was not a part of their perceived liturgical inheritance and they lacked the vision and leadership necessary to implement what Pope St. Pius X was envisioning.
In addition, the Protestant influence of the American culture with regards to religion was often one of “religious experience” or “spiritual feeling.” Because chant was different than what they were used to and because many American Catholics embraced the liturgical theological principles of Protestantism, the sacred music reform of Pope St. Pius X did not appeal to the “religious experience” of American Catholics. For this reason, many of the efforts to implement sacred music reform failed to take root and fizzled out without bearing much fruit.
Although the world has changed greatly over the past 114 years, we are still faced with similar challenges posed by modernism. There is a strong movement in our current American culture to become more secularized. If American Catholics are going to have the necessary strength to stand up against the assaults of 21st century modernism, we are going to need to rediscover the fullness of the gift of the liturgy, and enter into the Mass in such a way that we can benefit from the many graces that are made available to us.
Liturgical reform is rarely easy because it almost always involves a reworking of customary practices loaded with sentimental attachment. A committed liturgical reform involves a willingness to surrender our own preferences and desires (which are often the hardest things to surrender to the Lord). - Pope St. Pius X and Liturgical Reform