Edit: On review, I'm approving this, as youre asking a historiography question. But a reminder from the mods to keep it civil everyone :)

There are a few reasons:

• The writers at the time of the exile were not writing for the purpose of history as we know it. They were writing to illustrate truths about man (and God), and to explain from a theological perspective why the exile had happened. Although there are definitely truths to be found about human nature there, that isn't what modern historiography is all about. It wouldn't be a stretch to say that some of the events are true in a philosophical sense, but not historically accurate. "Truth", in this case, is largely dependent on how you define the word.

• There is no physical evidence of most of the happenings depicted in the Bible. There are mentions of a few figures from the Bible in other sources that are probably the same people identified in the Bible, but we can't be sure since they are brief mentions, generally only in one other sources. Proper historiography relies on primary documents (or secondary if that's all there are), but there just aren't many to support events from the Bible. There is support that certain people from the Bible existed, and that some of them were considered kings or whatever, but there's a big gap between "this person did exist" and "the story about him in the Bible is 'true'".