To put it simply, structures that have a wide base and sloping sides are the easiest structures to make tall without having any sort of reinforced material like our modern practice of setting steel rebar in concrete. These sorts of structures are not difficult to figure out on one's own once you begin piling materials in one spot. Think of going to the beach as a kid. If you fill your bucket with sand and continuously dump your full bucket in the exact same spot, a mound will form with a wide base and sloping sides. Building off of this simple observation, people can and did easily take this effect one step further by adding structure to the materials they used (blocks, bricks, sod blocks) or by packing materials and then covering them with more structured materials (earthen pyramids with limestone block facades, for example). There is no need, and no evidence, of people widely sharing how to build pyramids since such a thing is relatively easy develop and construct.