Welcome Libertas (I like the nickname
I'd put it in this way. Western Christianism as a whole, at some point around the 9th century and the Reformation, simply stopped believing in the power of the Holy Spirit as Spirit of Truth being really present and governing the Church in a literal way.
You see, when Our Lord is about to ascend to Heaven, He promises to send a Comforter, the Spirit of Truth who would make clear even many things He had said. He is the origin of both bishops and the Scriptures but He did not promise a bishop or a Scripture to be the infallible guide of the Church. He promised the Holy Spirit.
Now, let's step back a little from the metaphysics and think simply of the concept that the Spirit of Truth guides the Church. In a simple way, it merely says that despite different versions of Scriptures, and power-driven bishops, Truth will prevail in the end. In a sense, it is similar to what happens in sciences today. There are many very ugly power disputes among many scientists, for the top chair of a department, for social prestige. There are far too many cases of tampering documents and data to "prove" a point that will bring such power and prestige - the equivalent of changing the Scriptures or interpreting them in convenient ways. Yet, in the end, despite the various pesky mediocrities of bad scientists, of certain scientific institutions and of politicians and capitalists involved with it, truth prevails in science. There is no need for a chief übber head scientist with jurisdiction over all laboratories in the world or for an infallible scientific book to guide everybody. The trust is, and it should be, in the spirit of truth. Only if they knew it is more than a metaphor and that this "spirit of truth" is, really, "The Spirit of Truth" acting externally on them.
That is why people trust and respect science. Science trusts truth, loves truth and doesn't accept substitutes for it. If the "Universal Scientist" or the "Infallible Book of Science" were ever brought into the game, even if subcounsciously, people would notice that the need to bring up these things reveals the scientists would not be striving for truth anymore, just for legitimacy which is far different. Since theories and technologies would innevitably fail after some time, it would just further reveal the folly of those substitutes of the loyalty to truth and science, and its institutions would eventually loose all its credit with the people.
That is what happened with the Church in the West, both Romans and Protestants. In the place of the Holy Spirit, of the Spirit of Truth, they put respectively the person who used to be the first bishop of the Church and the Scriptures. They don't really trust that Truth, who after all is Jesus, can prevail of its own accord. For them, it needs a "strong man" or a "strong book".
To give an example, there were several cases in the history of the church when one or few saints prevailed - even if only after their martyrdom - against councils, bishops and false interpretations of the Scriptures. At other times, it was the councils or authorities that were used by the Spirit of Truth against the folly of individuals Other times even the whole Church was reproached by the Holy Spirit using non-Christians to bring them back to the right path. Sometimes innert objects were used miraculously by God to send His messages. In all this we see that the "Spirit blows where it will" and that it is the Spirit of Truth who is the infallible guide of the Church, and that the idea of an infallible man or book, no matter how important they are in the Church, borders blasphemy against the Holy Spirit, which is the unforgivable sin.
Now, that, of course, does not counter the fact that both bishops and Scripture are core "organs" of the Body of Christ. It is only that *they* depend on the Spirit of Truth and not the Spirit of Truth depends on them to be expressed in the world.