This is because the Old and New Testaments have distinct authors. We can divide the Bible up into chunks. Let's start by splitting Old from New, but also splitting the Pentateuch from the rest, and also separating the Epistles, as well as John and Revelations.

Now, let's go back-to-front. The Pentateuch is set in mythic times. It covers an invented history that includes features of myths of surrounding lands, like Great Floods [0]. The main feature, the Exodus, is set around 1200 BCE, and is a grave distortion of actual geopolitics around the time; in brief, the Egyptians conquered Caanan [1][2] around this time, occupying it until the Bronze Age Collapse. The occupying pharaoh, his capturing of Caananite princes, and his military presence created a long-lasting mythic impact.

Civilization needs a few centuries to rediscover how to read and write after the Bronze Age Collapse. During this time, records are lost, and stories are shared orally. By the 900s BCE, when historical records start to even remotely corroborate Bible stories, the Northern and Southern Kingdoms of Israel start to manifest. We don't know how many of the stories are true, but we suspect that many of them have some sort of historical roots, while simultaneously being exaggerated to fit fresh new nationalist themes. For example, stories of Joshua are highly exaggerated; the Jericho campaign took place not in the 700s BCE, but closer to 1500s BCE, and was carried out by Egyptians [3]. This sort of politicized editing of the Bible seems to have been present from the beginning of its editing [4][5].

And what else is happening? Conquest. Some guy from further north named Alex shows up and conquers a bunch, but then he gets a cough and dies. Another guy named Jules shows up and conquers a bunch too, but then he gets politically backstabbed. There's a gap of about half a millennium in the actual historical record, at this point, in terms of miracles.

In fact, now that we've reached the New Testament, it's worth reflecting: Who's writing this thing, anyway? It's no longer priestly Hebrew scholars, but Hellenistic Greek scholars [6][7] doing the writing, and they're sharing all of their sources so that their words will line up. In their painstaking work, they clearly show that they are intentionally quoting from the Greek version of the Old Testament, the Septuagint, famously mistranslating "virgin" and leading to a hilarious misunderstanding [8]. The Epistles, those are real enough, and there were folks traveling and preaching. The miracles, though, harder to tell.

Finally, we get to John and Revelations. Nobody's sure what's up with John. Revelations is clearly incoherent, although pretty. It is flabbergasting that these are the two books that seem to support folks' beliefs so often.

Hope this helped you look at the whole Bible.

[0] https://en.wikipedia.org/wiki/Flood_myth

[1] https://en.wikipedia.org/wiki/Battle_of_Kadesh

[2] https://en.wikipedia.org/wiki/Egyptian%E2%80%93Hittite_peace...

[3] https://en.wikipedia.org/wiki/Battle_of_Jericho

[4] https://en.wikipedia.org/wiki/Source_criticism_(biblical_stu...

[5] https://en.wikipedia.org/wiki/Deuteronomist

[6] https://en.wikipedia.org/wiki/Synoptic_Gospels

[7] https://en.wikipedia.org/wiki/Q_source

[8] https://en.wikipedia.org/wiki/Septuagint