Everything changed when JPII became Pope in late 1978. He came from Poland, where the Church was the only force countering the Communist government, and where one of the greatest demands on that Church was holding strictly to traditional principles any liberalism was seen as a concession to the Soviet-backed government and its hard-line atheism.
So, when JPII came to the Vatican, he brought that same mindset with him, and made it his goal to stamp out both liberalism and diversity of belief and the U.S. Church, along with that of Central America, was the main target of his crusade. This took the form of making sure that any new bishops were of his same hardline beliefs, and that any deviation among the clergy would lead to them spending their lives tending to a tiny parish somewhere in Bumfuck, Iowa or the like. As an understandable reaction to this, the number of young men pursuing a vocation to the priesthood dropped dramatically, and those spaces were taken by a new wave of rad-trads eager to return the Church to pre-Vatican II days, right down to the Latin Mass. Over decades, this policy, which was continued by BXVI, percolated through the U.S. Church, making sure that the official teaching on social justice being proclaimed from the pulpit was restricted to the sanctity of life (no abortion) and the sanctity of the family (no LGBTQ). Furthermore, during that time, the hierarchy of the U.S. Church (the U.S. Council of Catholic Bishops), having been filled with ultraconservatives through the Vaticans policies, became a close backer of the Republican Party, and formed a tacit alliance with the leaders of the religious right (evangelicals/fundamentalists not, as you imply, Protestants as a whole, as the mainstream denominations shifted toward the left during that same time period) to work together the latter would help Rome outlaw abortion if Catholics helped them do the same with same-sex marriage and reestablishing traditional family values.
This policy only really came to an end with the election of Francis
but its obviously going to take some time to reverse the situation caused by almost four decades of effort from Rome to establish an ultraconservative hegemony.