Because they believed it was true. Whether from witnessing or hearsay or historical markers or whatever (or my personal favorite - guidance from the Holy Spirit, as Jesus promised), that's what they recorded. They recorded the truth as they knew it.
And not all the Jews were guilty, of course. Only the hypocrites, the brood of vipers, the blind guides, the dead men's bones, and the like. Those who proclaimed Caesar rather than God as their king. The temple authority and the keepers of the Law. The Pharisees, their scribes, the elders, the chief priests, those who perverted Moses and preached an erroneous doctrine.