Why are people so concerned with what is supposedly “left out” of the Bible.....?

Those who do this do it because they think if they can invalidate what IS in the Bible they won't have to answer to the truths of the Bible.

NOT!

People want to know more than what is written in the commonly used canon of scripture because they want to know the truth, the whole truth so that it can set them free...

Jesus said that the promised coming of the Holy Spirit into His followers would lead them into all truth and that the truth would set them free... He also said that the Spirit would remind them (the saints) of the great many things which He had spoken to them while on earth - such as the things which John recalled but didn't mention in His gospel...

You're right. The last thing people need to know is the whole Word of God.

Better to give them an abridged version, more suited to their brief attention spans.

Anyway, it's not like Christians take God that seriously.

If they did, then the Bible would be whole, complete, unabridged, even if it meant it was so big that even God couldn't pick it up.

I think because those things left out would shed light on the rest -- and the fact that those left out (by choice of the early leaders) contradict what is included. I think there are many, many reasons people want to know about what was left out (and why it was left out), mainly so they can determine if it is something they can out value in to believing

Tha main persons to concerns themselves with what has been left out are the same people who question it's validity to begin with. These individuals still would be not be satisfied with a "complete" Bible. But, it is a useful way of casting doubt and scorn for those who do believe.

"I was always more concerned with the events that were Left

out of the Old Testament, than the New Testament."

"Absolutely nothing was Left out of the Book of Revelations."