Because the scientists weren't in charge when the decision was made. It was in part due the the influence of the McCarthists.

Just because the scientific advances are there doesn't mean the general populous is going to be scientifically minded. Even science seems to have broken down into a smaller community of it's own. Most people are still quite stuck in religious ideology and at the moment many of the schools are in poor shape, possibly too poor to pick up the slack and get to a more solid science and history based education.

I don't agree that America is very advanced in science, after all there are way too many flat earthers residing there.

The national motto is E Pluribus Unim, latin for "out of many, one."

In god we trust is a cheap bumper sticker slogan they added in the 50s to distinguish from the godless commies. Sort of like how most of the confederate monuments were even later in response to the civil rights movement.

Added in the fifties in response to the "godless communists".