It's because in the absence of the Bible, God reveals himself to people regardless, and he takes it from there. This is prophecy. If you believe the Bible is true, then you must believe this is how God works.
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The message of the Bible then is, repeatedly, to all people, for each of us to focus on our relationship with God. It is beyond question how much the admonishments in the Bible establish this reality.
So to those who don't know squat about the Bible, it's ok. You're not going to be in disfavor with God over it.
If you don't pray, well, yeah, that's probably going to be an issue. He is real with you. He expects you to be real with him. You have to do that to stay in relationship with him in some shape or form! :)
Knowing the Bible though ... eh, the knowledge in it largely confirms what God is already doing in a person's life. There are prophecies, and those are great. There are a lot of good things the Bible offers, but to feel like you just must know it in order to be close to God ... nah, that is the furthest statement from the truth.
Consider this, God himself (in the past talking about the future) said the following in Isaiah 65:1, "I am sought of them that asked not for me; I am found of them that sought me not: I said, Behold me, behold me, unto a nation that was not called by my name.", which was later quoted again in Romans 10:20, "But Esaias (Isaiah) is very bold, and saith, I was found of them that sought me not; I was made manifest unto them that asked not after me." ~ (King James Version of the Bible)
So there you have it from the Bible itself ... God makes himself known ... well, that is what the Bible is based off of afterall anyways ... it contains accounts where God made himself known to people and forecasted that he would continue to do so because that is simply his way. He has done that method with mankind since the beginning of humanity.
If when He reveals his reality to you, then you become the reality of what the Bible documents, which is better than reading what the Bible documents about other people it happened to you personally. At that point, you are in a relationship with God himself, but to where are you willing to go with him? Do you want to continue to head to his leading or go away from it. The Bible gives many accounts of both choices.
Unfortunately, accounts about God, especially the Bible have been used to craft a lot of different narratives to cause a lot of people to act in certain ways. This, too, has happened since the beginning of humanity frome the serpent, Even, and Adam until our present day - oral or written - God's words to mankind have been used for the wrong goals.
Just remember though. It is your relationship with God that counts to God; not your relationship with the Bible or others' accounts of God. Your understanding of God through them or the lack thereof, or other people's interpretations of what the Bible means is on the other folks. Keep your relationship with God clean.
Life on this planet is not about things like the Bible. It is about you and God, your Creator, having a relationship together that is mutually beneficial. :)