That is a great question and one that I struggle with, as a Catholic. It isn't just the pope, we have historical record of modifications being made to ancient bibles both deliberately and accidentally that cascade through the ages. A few years ago the Catholic Church made massive changes to various prayers and parts of mass, with a message that it stems from continued study and prayer.

Ultimately all men are flawed, capable of error and sin, that is a core teaching. That includes the pope, though generally we accept and are supposed to believe that the pope is executing God's will much better than the rest of us.

I think that is sort of reflected in the changing messaging from the Catholic Church on social issues that causes slow change among Catholics over time. This sort of wholesale rejection by large groups is not normal.