Why hasn’t everyone past the age of 8 figured out that religion is pure nonsense?

Yeah! Why? It kind of suggests that most people know something you don't know.

There is a genetic predisposition to internalize and believe without question things that are told to a child between the ages of 4 and 8.  This is evolutionarily favored: "Don't eat those red berries, children, they're poison."  But unfortunately, this mechanism can be used to instill beliefs that are extremely difficult to overturn later in life, beliefs that are so fundamental to a person's psychology that they'll warp their perception of reality to keep them in place.  And, of course, these memes are contagious across generations.  The memes of the major religious have evolved over the centuries to be maximally contagious in this sense.

Why haven't people figured out that prophecies in the Bible are being fulfilled and that they could only have come from God?

   Religion offers great comfort to people who are willing to suspend belief in empirical evidence.  I'm reluctant to criticize people who are in need of great comfort.

   Update @Thumbs-downers:  If you aren't suspending belief in empirical evidence, go ahead and produce some empirical evidence for the existence of a God.

 Because of lifelong, Peer brainwashing very obviously .

It´s sad.....
Dogs do not become  so afflicted though, and will readily herd sheep on any given day of the year . 

( Good able Sheepdogs are  trained better by far though )

Six decades ago (plus) I passed the age of 8. When I was 8 I was being indoctrinated by sincere parents who had fallen for the religion of an American cult. It wasn't until I was halfway through my second decade that I realized that that religion was worse than nonsense - it was dangerous deception. I left it. But I knew God wasn't nonsense, and He answered my prayer which caused that departure. However, I wasn't left in a vacuum. God led me to understand what He says about the person of Jesus Christ, His beloved Son, and I became a follower of the risen Christ - a Christian. 

Since then, I have seen much more of the dangers of mere religion and have stuck to avoiding any religious systems that claim to get you nearer to God, because none of them do. Only by being found "in Christ" can we get close to God and that is what I have learned. 

Religion is the heart of a heartless world. It helps people to numb the pain of living in this world. 
You will not realize unless you experience it.

If it is not important to you, why would you care? You don’t need to dictate the beliefs of others. 

No one can "figure out" something that isn't true.

People feel they need something to give them guidelines to live by and that’s why they choose to believe in religion. Many religions in themselves do give a good set of guidelines, but people misconstrue those and religion is one of the biggest causes of war in the world.