Sufficient information has been out there for over 3500 years. The proof is in the billions who have indeed believed. The main reason it hasn't been heard by the other billions is people not wanting to hear (and Christians not wanting to suffer enough to tell them). In the Internet Age there is no longer any excuse.

But even the Apostle Paul asked your same question 2000 years ago:

"Everyone who calls on the name of the Lord will be saved." How, then, can they call on the one they have not believed in? And how can they believe in the one of whom they have not heard? And how can they hear without someone preaching to them? And how can anyone preach unless they are sent? As it is written: "How beautiful are the feet of those who bring good news!" - Romans 10:11-13

And Isaiah 2700 years ago.

But not all the Israelites accepted the good news. For Isaiah says, "Lord, who has believed our message?" Consequently, faith comes from hearing the message, and the message is heard through the word about Christ. But I ask: Did they not hear? Of course they did: "Their voice has gone out into all the earth, their words to the ends of the world." - Romans 10:14-19