Why were the pyramids constructed in different shapes?

Answer 1

The pyramids in Egypt were all built the same way. They were square based and in porportion to the golden ratio.

Although pyramids in the Middle East and Persia, mor commonly known as ziggurats, were round and tiered. This is because they were built by a different civilization and in a different time pyramid. And also, the South Americans buit square based tiered pyramids, because they too had different architecture methods and lived in a different time period.