What you mean less people have faith in the veracity of a book with talking snakes and giants in it?
Okay, that was a bit snarky, so let's try again.
If EDUCATED Americans are less inclined to believe in the Bible as the literal word of God, it's because they now know that stuff in the bible isn't true. We know we evolved from primates, not created from clay. We've done the archeology, and we know that Hebrews never lived in Egypt under the Pharaohs, that the Philistines were part of an invasion of the Sea Peoples in the 13th century BCE, and that Yahweh was just one of many gods worshipped in the ancient Levant.
Sadly, backwards Bronze Age superstitions won't go away because people are terrified of death, and live in fear of the end of their linear existence.
Now, one can look at the bible as what it is, a bit of historical fiction, with maybe some real characters in it, and still draw positive messages from it.