A lot of factors there.
1) Why were they built? They aren't a house or office building. They are very large for what and for who?
2) The precision of the stone blocks is unfathomable at that age of our understanding of human development. World class construction companies have said they would not even attempt to create such a building today. Some sites with 1000 ton blocks. And for what/who? How did they achieve such precision with out our modern day machines???
3) Why did cultures all over the world independently develop such similarities with now way to communication with each other at all? No, it was not a planet wide pyramid competitions - you'd think so, but no.
It really goes beyond they all did that own their own. There is a true black-out period around 0 BC/AD or BCE/CE where science and technology had a complete reset and started from scratch. Today no one can prove what the great pyramid is or how it was built. Sumerians documented Pluto 10,000 years ago - we just found it about 1930ish. How is it explained?