Because the Catholic leadership is fully liberal.
Why pick fights with your Catholic allies?
I reflexively agree with you on most issues and I am, have always been and always will be Catholic. Now you might say that I am not in "leadership" and that would be true.
OTOH, there are many Catholic leaders with whom you may agree on much: Michael Novak, the retiring Francis Cardinal George of Chicago, Raymond Cardinal Burke, Archbishop Charles Chaput, Archbishop William Lori, Archbishop Salvatore Cordileone, Bishop Daniel Jenky, to name a few.
You would find yourself in substantial agreement with the Knights of Columbus and its Supreme Knight Carl Anderson, formerly of Reagan's White House staff, and the previous Supreme Knight Virgil Dechant, a long time conservative Republican in Kansas.
I grant that there are numerous regrettable figures in leadership in the US Catholic Church: Sean Cardinal O'Malley, Donald Cardinal Wuerl, incoming Archbishop Blaise Cupich, Bishop Robert Lynch, come immediately to mind.
Because of the failure to date of internal warfare in the Catholic Church, we have yet to establish a refusal of sacraments to those "Catholic" public figures (where one was baptized as an infant is not everything) who have effectively excommunicated themselves from the Church by their material cooperation with abortion or cheerleading for it: the late Ted Kennedy, John French Kerry, Nancy Pelosi, Rosa DeLauro, Patty Murray, Jerry Brown, Dannel Malloy, Patrick Quinn, Anthony Cuomo, Mario Cuomo, Edward Markey, Susan Collins, Patrick Leahy, Martin O'Malley, and so many, many others. OTOH, those who are not Catholic cannot be described as "Catholic leaders."
A list of relatively recently (last 50 years or so) deceased Catholic leaders include such noted conservatives as Bill Buckley, Frank Meyer, Friedrich von Hayek, Clare Booth Luce, Professor Warren Carroll, Russell Kirk, Senator Joseph R. McCarthy.
The Catholic Church, as an institution, has always been favorable to organized labor, recently favorable to immigration and favorable to social spending projects which include neither abortion nor homosexuality. OTOH, any Catholic worthy of the name Catholic leader has been quite opposed to Marxism in all its forms.
In short, it is a gross overstatement to say that "the Catholic leadership is fully liberal." Not at all perfect but certainly not fully liberal.
God bless you and yours.