My understanding based on my biblical studies is that the default position after death for a human is hell - separation from God. It is only through God’s grace anyone is saved. If you think of Heaven as analogous to God’s home why should he let anyone in His house if they don’t even accept that He exists.
But what about tribes and those who never knew about Jesus? I have no idea. It is in God’s hands not mine.
If you think of Heaven as analogous to God’s home why should he let anyone in His house if they don’t even accept that He exists.