So the biggest historian and friend to the royal house of Judaea and a contemporary of Christ's time completely missed Jesus, the condescension of god to man? It could have happened. But that's like Fox News missing the overthrow of Iraq.
Arguments from silence are unreliable. Josephus is a great Jewish historian of that time too and he wrote about both, Philo and Jesus Christ. Josephus was in Jerusalem, while Philo was far away in Egypt at the time. According to Josephus, Philo also had lots problems of his own at the time to worry about Jesus(see below). So if Philo did not mention Jesus, then we shouldn't be surprised as he was too far away and too busy at the time. And there is always the possibility that Philo did write something about Jesus, but it was lost.
"There was now a tumult arisen at Alexandria, between the Jewish inhabitants and the Greeks; and three ambassadors were chosen out of each party that were at variance, who came to Gaius. Now one of these ambassadors from the people of Alexandria was Apion, (29) who uttered many blasphemies against the Jews; and, among other things that he said, he charged them with neglecting the honors that belonged to Caesar; for that while all who were subject to the Roman empire built altars and temples to Gaius, and in other regards universally received him as they received the gods, these Jews alone thought it a dishonorable thing for them to erect statues in honor of him, as well as to swear by his name. Many of these severe things were said by Apion, by which he hoped to provoke Gaius to anger at the Jews, as he was likely to be. But Philo, the principal of the Jewish embassage, a man eminent on all accounts, brother to Alexander the alabarch, (30) and one not unskillful in philosophy, was ready to betake himself to make his defense against those accusations; but Gaius prohibited him, and bid him begone; he was also in such a rage, that it openly appeared he was about to do them some very great mischief. So Philo being thus affronted, went out, and said to those Jews who were about him, that they should be of good courage, since Gaius's words indeed showed anger at them, but in reality had already set God against himself."
[Antiquities of the Jews, xviii.8, § 1, Whiston's translation (online)]