There is an almost unlimited number of things that each gospel writer does not mention. Each writer chose their material carefully, producing a very compact story of the events they considered most important. We could just as well ask why Paul did not mention Jesus’ appearance to the disciples on the way to Emmaus, or why John does not mention his appearing to the disciples in Galilee or any other number of events that each gospel writer did not choose to include. The only important criterion is this: Is it reasonable to believe that Paul is lying to the Corinthians about Jesus’ appearing to more than 500? The answer is a resounding no!!! In this passage Paul is telling the Corinthians this: If you don’t believe me, ask one of those 500! It is ludicrous to propose that Paul would have invented such an easily-refuted claim as this. Could he have invented his own visitation by Jesus? Possible so, given that he was the sole witness, but not likely. Could he have invented the visitation to more than 500? Certainly not!
Why would Jesus have appeared to Pharisees? Which ones? When? For all we know, perhaps he did, but the evidence is that Jesus only appeared to believers, not to those who refused to believe in him. The exception, of course, is the Pharisee Paul, who Jesus did appear to! Your question seems to imply that, for some reason, Jesus should have appeared to unbelieving Pharisees. I see no compelling reason he ought to have done that. The idea that he would have appeared to Pilate seems to me extremely far-fetched. Far-fetched, indeed. With what conceivable purpose, given that he only appeared to Jews!
Would Jesus appearing to Pilate have changed his mind? Who knows. But then again, Jesus could appear to you or to me or to Hitler or to Michael Jordan. Jesus does not manipulate people into believing in him by random appearances. The angel who walked in the furnace with Shadrach, Meshach and Abednego did so to encourage the youths, not to convert Nebuchadnezzar, and I assume that their survival in the furnace would have been compelling, even without the extra figure in the furnace. In any case, I trust God to make the right decision as to who he ought or ought not to have his Son Jesus appear to.
John Oakes