The reason why the Egyptians change up design and augment is ??
The Mesoamerican paradigm may have changed from structures used initially as tombs, then astronomical observatories, then to temples of worship, followed by places of sacrifice and finally to finish (Western invasion).
The Egyptian parallel is different. Assuming that these structures were Mesopotamian in character. It may have been tombs, then ziggurats then pyramids. So, the usage goes from sacrificial to astronomical to ascension to tombs to finish (Western invasion).
Menkaure is a good example of these changes over time.