They did appear to write about Jesus but they both were born after Jesus died, which means their accounts were at best second hand.
Ok, so any scholar who wrote about figures just before their time are not good sources? First, Tacitus lived right after the death of Christ. Second, he was known as a great historian, so he wasn't going to make anything up, especially when he didn't care for Christians. There are many scholars through the years who have written about past figures, but they aren't deemed to be untrue.