Roman historians didn't mention Jesus more because he wasn't significant to Roman history — they didn't even mention Pontius Pilate, known only from Philo, Josephus, and NT sources

Roman historians focused on Roman affairs of Roman significance. Pontius Pilate — the prefect/procurator of Judea — is not mentioned in any Roman sources of the first century. He is known only from Philo, Josephus, and New Testament literature. Pilate mattered to Jews and Christians, not to Roman historians. The same principle applies to Jesus.