Philo, a Jewish philosopher, lived from 20 BCE to 50 CE. He never mentioned the crucifixion. Why do we believe Josephus who mentioned Jesus long after he lived, but ignore Philo?
We have no idea of whether Philo ever mentioned the crucifixion or the three hours of darkness. I assume that we only have a very small fraction of all the things that Philo wrote. Let us imagine that someone took a collection of 40 or 50 texts or e-mails you wrote. Let us also imagine that you never mentioned President Obama in any of these texts or e-mails (a very high possibility if we choose only 40 or 50 at ramdom). Is this evidence that Obama was never president. Not at all. The lack of particular mention of a particular fact from a highly selective portion of what one person in the first century wrote is NOT evidence that that fact is true. Lack of evidence is not evidence of lack. This has always been true.
Again, I have no idea if Philo ever mentioned the miracles of Jesus or his crucifixion.
Put it the other way. Let us say that in the 40-50 texts or e-mails you mentioned that Obama was president. Would this be evidence that Obama was president? Absolutely!!! This is why the mention of Josephus and Tacitus is evidence for Jesus while the lack of mention by Philo is not evidence against his crucifixion–especially because we really have no idea whether he actually mentioned Jesus and his crucifixion, given that we have only a small portion of all he wrote or said.
By the way, you say that Josephus and Tacitus lived long after Jesus. This is simply not true. Josephus was born about AD 37 and wrote about Jesus during the first century. Tacitus was a contemporary of Josephus. Both lived at a time when most of the eye-witnesses of Jesus’ life were still alive. This is definitely NOT a long time after Jesus.