Per given volume, the pyramid is the most stable shape with the maximum height
Pyramids have a consistent low center of gravity, the idea is they can be built to infinity with an ever widening base. Pyramids naturally occur in nature as a stable place for sediment to build up in the form of mounds. For example, imagine digging a hole in your backyard. As you dig, the removed dirt piles higher and higher. If you placed this dirt in the same area the resulting shape would be a pyramid like mound of loose dirt.