Imagine being a species that is so evolved that they knew that the longest way to live was to eat healthy and exercise daily, but instead of exercising like we humans do now they all worked together on lets say their work out "Hours" to help construct and advance the human path so later humans will look back and say, Hey we can do that too. Only to keep this cycle of Humanity as or even more as the last cycle of Humans.
Now look back at all of the people who help put together these pyramids for maybe these amazing leaders. They put them in their tombs not to show how weird and mysterious they were, They put them in there to show that they were such good leaders that they should be remembered for ever. Just think, Everyone is using their spare time to help put together something so amazing for someone so great.
What im trying to say is what if there were advanced civilizations before the people who made the pyramids, But they got so advanced that they "Dumbed down" because they didn't need earth anymore. What if the left only the ones that were not fit, and mentally capable of working together to regrow the population to the point that the next advanced wave of humans will too leave the planet for good one day. Just think about it, one day we will be out of this solar system and eventually we are going to have to leave some people on earth for a what if scenario to restart life on earth again. We are already going to outer space, soon enough we too will be like the Egyptians. Maybe even better... Only time will tell