The gnostic gospels were studied way back when the Bible was being canonized. They were rejected because they were not in harmony with the rest of the text. They in fact contradicted major issues. Also, they were written hindreds of years after the fact. For example, the gospel of Judas was written in the 3rd century, long after the Christ was crucified and Judas committed suicide.

They are an interesting glimpse into the history of the church tho.