Individuals build empires because they want their names to echo through time. They build massive constructs of stone and steel so that their descendants will remember the people who created the world that they only live in. There were buildings on Earth that were thousands of years old, sometimes the only remaining evidence of empires that thought they would last forever. Hubris, the professor had called it. When people build, they are trying to make an aspiration physical. When they die, their intentions are buried with them. All that's left is the building.