I suspect that having established the Bible as the ultimate authority, some people don't ever read anything else on the subject. There is a great deal to learn about the things mentioned in it from other sources, which throw light on the events from different sides, making things a lot more three-dimensional than they can at first appear.
There is a lot to learn about the history of the actual writings, too,
How what is in them (particularly in the OT) began as oral tradition, handed on by people who had memorised them for telling round the camp-fire to nomads who could not read. There must have been many places where they remembered the bones of the stories but not the flesh, but they told them to make them come alive to their hearers.
How they came to be written down years, sometimes centuries, after they happened, and were modified by others from the very start, so what we read is not necessarily what was first put onto paper.
How successive hierarchies pruned out the bits they didn't like, the bits they believed were false, the bits that seemed irrelevant.
How it was changed from the original language into others - into Greek or Latin, and from those into the language spoken in each country at the time of the translation, with an accumulation of inaccurate translation, local bias in interpretation, political influence and so on.
And always there is human fallibility. Human hands, writing human words, heard by human ears and interpreted by human hearts.