Since the arrival of the Anu, human cultures have been strongly influenced by their teachings. Pyramid shapes were common to deflect the incoming energies. Great open spaces were needed for the carriages of the Gods. The Anu had been an integral part of human societies for as long as humanity could remember.
When humanity started re-building after the cataclysm, many of the Anu teachings were still part of their cultural heritage, and of their mythologies. So of course, when they started building their great cities, they built pyramids and landing platforms.
Without any personal knowledge of the systems they were imitating, most early civilisations ended up as cargo cults without function.