The gnostic gospels are interesting. The problem is that they are contrary to the historical facts contained in orthodox Christianity. They were written several hundred years after the life of Christ. Because of the substantial differences between them and the original gospels they are viewed more as allegorical fairytales.
Two obvious problems among many is the fact that in the gospel of Thomas, Jesus is described as married to Mary Magdalene. This contradicts what we know about the life of Christ, that he remained single. Second, unlike what you call it, gnosticism does not mean knowledge, but special knowledge. Gnostics believed that only a select group had it. Those with special knowledge therefore became the only ones to be fully reconciled to God. Again, this is contrary to the gospel message that all who believe will be saved.
The fact that the organized church rejected Gnosticism is to be expected. It’s authority and truth are questionable, though there is much to be applauded in their beliefs. In saying this I am not trying to justify the Bible as the inerrant word word of God. It is full of contradictions, historical inaccuracy and hateful standards no one would accept today. Further, much of it attributes very ordinary, natural phenomena to the hand of God at work in the world. A lot of it is based on ignorance. But when it comes to the gospels, those events were witnessed by tens of thousands and have been verified time and again. The events of 2000 years ago were so extraordinary and witnessed by so many people, that the historians of the day were forced to acknowledge their validity. Something very extraordinary happened on the cross 2000 years ago. The power of any religion is its life affirming proclamations. The call to love, respect, and treat everyone with kindness and generosity is something that resonates in all of us. That is the importance of the authentic divine message whether derived from traditional Christianity, Gnosticism or some other faith tradition