This is a fair point. At the same time, we have to keep in mind that Israel was at this point a minor footnote in history. They had been conquered many times, and as a result didn't get much attention from Rome, which is why they put the Herods, a family of puppet rulers, in power -- the region didn't merit much attention. Additionally, there had been several Messiah-wannabes, all of whom had been put down remarkably easily by Rome.
This is where some of Aslan's assertions or critiques start to fall apart. Jesus' teaching style, as set down in the Synoptic gospels, reflects Stoic thought, as well as Hellenistic influence. ("Render unto Caesar what is Caesar's," etc.) Hardly the impoverished, nationalist zealot Aslan says he was, and indications that He may have actually hewed much closer to middle-class Jewish hellenism. (Which may have been reflected by his followers, which is what Rodney Stark argues in "The Rise of Christianity.") Additionally, there is evidence (again from the texts) that Jesus repudiated the idea of a politicized Israel. ("My kingdom is not of this world," etc.) His cousin John eventually adopted a more zealous, political methodology (attacking Herod Antipas for marrying his brother's sister), and was thrown in jail and eventually beheaded. Jesus, by contrast, distanced himself from this movement -- which may in fact have led to his betrayal, since there is evidence that Judas Iscariot may have been part of the zealot movement and had hoped that Jesus' movement would be more political.
In any event, Jesus would not have gotten much attention from the Romans, and it's clear that He didn't. In fact, the Jewish religious leaders -- who understandably watched Jesus' rise with great concern, since if his movement continued to gather steam, he could have become a political threat to their power (they were trying to keep Rome pacified in order to preserve some semblance of Israel as an independent nation-state) -- had to charge Jesus with a political crime in order to get Rome to pay attention to Him, and settled on sedition. But it's clear that Pilate had no interest in convicting Him, which shows that Rome had not yet paid Him much mind.
All of which says that the death of Jesus got very little attention from Rome and her historians. He was somewhat of a minor footnote at best -- an insignificant leader (in their eyes) of an insignificant country in a relatively insignificant part of their empire. Hardly the stuff of history. It wouldn't be until much later, when His followers had grown and "filled the earth" (to quote from Acts), that they even realized who He was...which is why it was only many years after His death that Romans started referring to His followers as "Christians" (initially a somewhat derogatory, mocking term meaning "little Christs").