Yup… back ‘in the day‘ most people didn’t have books.
The ones that could afford a book, would buy a bible. Funny old days.
For years The Bible was the only book most people had access to.
That’s why it’s the good book. It was the only book. There were no others.
If you tried to get a good science book in your collection of two, you’d probably be burned for witchcraft anyway.