I can see that argument. But there has been many holy writings over the course of creation. Why do we know that the bible is the actual word of God?
For one thing, it is the record of a people and God over many hundreds of years, even thousands. There is continuity and It traces the development of events and ideas. It is not simply a book of inspirational writings, which is what the sacred writings of many other religions use.
For another, it is provable (or, contrarily, could theoretically be disproven), so this gives us the reliability element...which again is missing from any of those other sacred writings. The Bible has been challenged many times and has stood up to the criticism and doubts. If it
is reliable, then we can believe what it says about itself...which is that it is divine revelation.
Shouldn't God reveal himself to them? Like say for example that an Indian tribe in Africa prays to God every single day. Yet they do not know who God genuinely is. They just worship God (and probably false Gods as it is further angering God more) shouldn't God reveal himself to them so that they can worship the true God and creator of the universe? You would think that the true creator of the universe would want the entire world to worship him instead of so many cultures and religions worshipping false Gods and false religious practices.
The answer to this very understandable question is that it is not our responsibility--or even something we CAN answer--to explain every last thing that God does or intends or how. Much of it is beyond our comprehension anyway. But Scripture is given for us in our own lives and we can live by it (which I think is the main question you were asking).
I mean you could argue that it is our job as Christian's to introduce these people to God like Paul did to the Roman's and Greeks but humans can only do so much. God can do anything. Yet it seems like God only reveals himself to those whom he chooses to reveal himself to. To me that's kind of inefficient and it gives atheists an argument for God doesn't exist.
I know, but we really cannot make God into a human with the same failings, purposes, and all of that, which is what you are unintentionally doing there. God is much beyond all of this, just as eternity and omnipotence are. But, for some reason, we don't question them. We do second-guess God, though, because we tend to picture him as if he were a superhuman rather than the Almighty.