There were just a bunch of different texts.
At some point (really two points: the Septuagint for the Old Testament, and then VERY RECENTLY King James for the New), a powerful group of HUMANS decided to put together a Book, and they included texts they liked and threw out others they didn't like.
How was it that this group (or these two, I'm not as familiar with the assembly of the septuagint) was so powerful? Please establish this. I don't believe they were very powerful as we see it. They may have been as powerful as say, Billy Graham, influence and all. However they weren't government leaders, had no armies, no weapons. How do you say they were so powerful.
Yes they were humans. I have said before that humans are a necessary part of the equation, however, they began from a source, which claimed to be the Word of the Creator. They were able to agree upon what parts truly were valid, as you can see from these posts, a significant task, and the protestant church agreed endorsed them for the next 400 years or so.
The criteria they used for including and excluding text is available and a very interesting study. I can't recall the references off the top of my head this moment, but I can produce some if you are interested.
The evidence doesn't seem consistent with just wanting to put together a book. These people endured ridicule, torture, and death in some cases to assemble a book that they believed to be God's word. Nothing evidences an ulterior motive of glory or fame. The fact is that they didn't receive glory or fame, then or now, only the product lived on without them. Could you name any of them without looking it up? If you can, you are knowledgeable. I suspect 99% of the population couldn't name one of them.
How about the equally maintained and holy-written books that didn't make it into the final cut? What OBJECTIVITY??? You think King James hired people for their Objectivity? How come they left out the Gospel of Thomas (by the Apostle Didymos Judas Thomas), for example?
I am not qualified to answer that question, about Thomas specifically. They did document their criteria and I have examined them indidually from time to time. They used solid bases to choose. I believe that they doubted the authenticity of that book. They would have otherwise likely accepted it on the grounds that Thomas was a legitimate Apostle of Christ.
And what are Song of Solomon and Revelation doing in there at all?
You don't think Song of Solomon is about RELIGION, do you?
Long long after it was written some rabbi made up a lying filthy untrue interpretation pretending it had to do with man's love of God, when any teenager can tell you what it's about:
"4 My beloved put in his hand by the hole of the door, and my bowels were moved for him.
5 I rose up to open to my beloved; and my hands dropped with myrrh, and my fingers with sweet smelling myrrh, upon the handles of the lock.
6 I opened to my beloved...."
Many of the books aren't particularly "about Religion". I believe the fact that the Song of Solomon is included is a testimony to the practices of those who included books. Leaving Song of Solomon out on the basis you state, not about religion, would have been consistent with wanting to create a religious book. It seems they left it in based upon its veracity (thanks for the previous grammar lesson), not its content (consistent with an attempt to actually, rationally discern which words were from God).
Perhaps God included it to show that sex isn't nasty, as you say (the words are really much stronger in the hebrew and greek than those you used - I think you'd like them).
As to Revelation, you give no basis for why it shouldn't be included. It was Apostolic (John) and appears to have been consistent and had a good audit trail for authenticity. It, unlike perhaps Song of Solomon, is very religious and is extremely linked with other (independently written) books.