Because the Catholic Church is a profoundly liberal institution that preaches a profoundly liberal gospel. For instance:
1) The Church teaches that nobody is beyond redemption. This is easy to say but more difficult to countenance when we really face up to what it means. The Church is willing to forgive the sort of transgessor that ordinary, decent, upstanding, respectable people would be willing to rip apart with their teeth and fingernails.
2) The Church, to the chagrin of iconoclasts of every creed, encourages sacred art.
3) The Church encourages frequent communion-- a practice that has been misguidedly attacked by those who consider it impious and irreverent, such as the Jansenists of the seventeenth and eighteenth centuries.
4) The Church has always proclaimed the dignity of all human beings. This is more or less fashionable now, but when it has been less fashionable-- for instance, during the Spanish conquest of South America or during the Nazi era-- the Church has resolutely proclaimed it.
5) The Church, unlike gnostics both religious and secular, believe in a public revelation that is available to all, as opposed to esoteric knowledge and hermetic secrets.
6) The Church proclaims the goodness of all created things-- including food, alcohol, sex, wealth, technology and art.
7) The Church has always had a special love and regard for the poor. The poor tend to go in and out of fashion with the intelligentsia, depending on whether Social Darwinism, Marxism, anarcho-capitalism, or some other doctrine is the ruling orthodoxy. "I have never had any feelings about the English working classes except a desire to abolish them and replace them with sensible people"-- Bernard Shaw.
8) The Church is willing to put its prestige and credibility behind Marian apparitions and miracles that have happened in modern times. If this isn't radical and daring, I don't know what is.
9) The Church is willing to take radical and controversial steps such as the introduction of the vernacular Mass and the blessing of Catholic Charismatic Renewal movements. Those who think that the Catholicism should "move with the times", and those who believe that it should be essentially a solid and unyielding fortress against the times, have both got it wrong.
10) The Church lays down conditions for the just conduct of warfare, and does not believe that, when the enemy is sufficiently dastardly, any measures-- torture, terrorism, total war-- are justified.
"Liberal" and "conservative" are useful words, and we can't really do without them. They mean different things in different contexts, and in most of those contexts, I would be very much a conservative and not a liberal.
But it is good to remember, from time to time, that liberalism and conservatism properly understood are both admirable ideals.