The last visit was supposedly about 2,000 years ago. That's a long time between hellos.
For God, there is no time, every time is now, there is no past, or future, just the present. So 2000 years ago, 200 years ago 20 years ago, what's the difference? And I doubt people would believe even if he did show himself. People don't believe in NDE's even though many of them have staggering amounts of proof behind them. There was a man in the 1800's who went around recording people's last words before death. People said they saw Heaven and hell. And still we don't believe. "What if they were lying?" we say. People didn't believe in Jesus even though hundreds of people saw Him resurrected. People won't believe no matter what. We always want to find a way to say "no, there must be a loophole." Like Jesus said, "If they won't listen to Moses, then I tell you even if they were sent a person from the dead they still wouldn't believe." And also, "If you don't believe in the words of Moses, then how are you supposed to believe in the Son of God?"