What do you think of the lost Gospels and why do you think they were rejected my main Stream Catholics ?

It would be almost impossible for any new books, Gospels or otherwise, to be added to the canon of any organized Christian denomination. The Gospel of Thomas would be the most likely candidate, but if you read it, you will see why it won't make it. The "lost Gospels" that I have read simply don't measure up to the New Testament four. I think the early Christian councils did a pretty good job of selecting the best of the lot.