Its a good question Ray! Why don't they keep in contact with us? If UFO's sightings are real, why don't they just land the spaceship and say hello? If there were ancient aliens, why not leave some definite proof for future generations like ourselves so we know they came here?
Maybe they did leave the proof behind!! Things like the pyramids and other ancient monuments around the world. Maybe they did get out of the spaceship and say hello...... Who exactly was Jesus in the Bible, and all the other bible Prophets? The bible says he came from the sky, the heavens. What about all the other bible stories? Maybe they were all stories written by men who simply could not explain the incredible things they were seeing, science being preformed by people who were far more advanced than them. But in reality, these gods were not gods at all, they were just scientists from other planets with more advanced knowledge than the humans at that time.
If they came back today, we will be better able to understand their science. But they might be afraid of our powerful military countries shooting down their craft or killing them.
Those pyramids are so mysterious! And ancient China is full of stuff too!
And what about this very recent UFO sighting over Xiaoshan Airport in Hangzhou, China on July 7th 2010;
http://abcnews.go.com/International/ufo-china-closes-airport-prompts-investigation/story?id=11159531&page=1Also on youtube;
http://www.youtube.com/watch?v=xP5DwFtFhyMSounds like the aliens are coming back and they checking out Xiaoshan Airport as a landing spot!
John.