This question first came to my mind when I learned about the giant size of the Giza pyramids and later when it turned out that the builders were not slaves, that (according to the recently discovered writings) there were teams who raced between the title of the fastest in bringing the next block up. The motivation cannot be explained by the ambitions of the pharaohs only, I think.
Then the same question popped up when I learned about Stonehenge and, recently, about Göbekli Tepe. Why spend so much time and energy? What was the motivation?
Well, today we spend a lot of money and efforts on the projects that do not demonstrate the immediate utility and do not have an ambitious individual (who could claim the bragging rights) behind them. The most expensive project ever is the International Space Station — $160 billion (the USA $60 billion, Russia $12 billion, Europe $5 billion, Japan $5 billion, Canada $2 billion, and the cost of 36 shuttle flights to build the station, mostly financed by the USA; China wanted to participate but was not allowed).
Large Hadron Collider built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and engineers from over 100 countries, as well as hundreds of universities and laboratories for $6 billion. The operation cost is $1 billion annually. Only the electricity bill runs up to $24 mln each year.
Why? Because each of us (well, there are probably exceptions) would like to know how the world is constructed and what is the place of humanity (including the tiny-tiny spec of me) in it. The ancient folks created those giants “experimental devices” to answer the same — the most important — questions.
Otherwise, how are we different from any other — moving or not — object of this world?