Oh, the similarities don't stop there, at least in the examples I've researched. Namely, the Egyptian Pyramids at Giza, the Mayan Pyramids at Chichen Itza, and the Khmer Pyramid at Kol Ker. In addition to sun worship, I've found the key feature to be the veneration of water cycles.

The Pyramids at Giza, built around the template of the earlier Elephantine Island Pyramid, are ultimately aligned with the sunrise on the date when Sirius appears on the night sky - signifying the start of the annual Nile flood. It might not seem like much to us, but in the absence of modern fertilization techniques, the Nile's ability to revitalize the soil was considered nothing short of supernatural, and a sign of the gods' favor.

The Pyramids at Chichen Itza are tied to the annual water level cycle of the cenotes - underground water reservoirs that are the cornerstones of Mayan agriculture. Again, simple to explain in modern day, but to the ancients, their ability to refill themselves every year was all but magical.

The Pyramid at Kol Ker was actually part of a large temple complex near the Tonle Sap lake. It appears there was a substantial rice field irrigation system around the lake and the complex.

My theory is, these pyramids in particular were designed as a kind of ritual calendars or sun dials, meant to track celestial bodies as a way to tell the exact date of the year for annual flood events. Even without the religious trappings, matters of agriculture were literal life-or-death affairs to the ancients, so you can understand why they were so venerated, and why so many people were eager to work on their construction.