Why isn't Thomas in the Bible?

The early Jesus movement was factionalised and there were varying stories regarding who and what Jesus was. Once Athanasius made his declaration then gospels like Thomas were immediately outlawed. That there were alternative gospels is confirmed by Christian champions like Bishop Irenaeus, who spent their whole lives dismissing and undermining the viewpoints that the alternative gospels expressed. This was the early church driving for uniformity of understanding and doctrinal consistency.