After centuries of exhaustive research of technical texts and ancient documents, professional historians have finally come to a clear understanding of the forces that shaped the ancient Egyptian pyramids. The missing piece of the puzzle turns out to be ... <dramatic drum roll> ... Project Management.
Modern PMs (Project Managers), most especially IT PMs, appear to be direct descendants of the ancient ones, at least analogically if not biologically, in mindset whether accidentally or purposefully.
In IT Project Management, a PM is designated by either a customer or a stakeholder (the ones who hold the stake over the mere coders' hearts whilst the PM wields the mallet). Requirements and features are carefully defined to be as impossible as possible and both the budget and timeline become written in stone. (Do not mistake this step to be metaphorical. This practice has been in use since before the pyramids and shows no sign of changing to a stoneless system.)
All this pre-work is completed before any people are chosen who will actually perform work, as their input might bring a chilling dose of reality into the situation.
This is the process that was used in ancient Egypt and continues to be used to this day, except that the PMs of the time decided to try a new PM methodology called 'Agility Construction' (in modern times the label has morphed into the 'Agile Methodology').
As with all successful projects, these ancient constructions (new constructions at the time) were tracked through the use of standard 'metrics' like 'Adherence to budget', 'Adherence to schedule', 'Value delivered' and 'Employee mental breakdowns'. As with all project management systems, the PMs get involved very early to be certain that metrics are designed into the project that have sufficient 'Play'. 'Play', of course, means providing a way for the PMs to 'play' the system; continue to look good in reporting no matter what the state of the project actually happens to be.
Herein lies the secret of the development of the shape of the pyramids.
We must, as always, begin by defining our terms. The word 'pyramid', as any dietician can tell you, means: 'to pile food as high as possible without allowing any "better-tasting" food to slide to a lower level, keeping the best-tasting food in convient reach at the top'.
However, the dieticians of ancient Egypt did not have a lot of really tasty treats available, so most of their 'pyramids' tended to be relatively boxy in shape. It was not until the invention of pastries and chocolate that food pyramids began to assume their current shape.
The ancient pyramids shape predates that of the current food pyramids for entirely different reasons, but were almost Nostradamously accurate in prophecising the eventual wealth of heart-hardening, cholesterol-laden goodies.
One largely standard set of requirements and features list from ancient times translates thusly:
I, Pharaoh Toulouselautrec, want...
A 16-room building that will thwart any attempted thievery, be completely weatherproofed, eminently dangerous to guests and must last FOREVER.
It must occupy a square piece of land 750 feet on each side, in a nice location, and be 480 feet tall.
It must be impressive to see even from a distance and provide a passageway that will eventually allow me to leave it to join the other gods.
It must give my wife the mother-in-law room she wants at the top, but don't worry much about the size.
The key here, the pointer, are requirements two and four. Can you spot it?
The savvy PM of the time realised that he could stay within the impossibly small budget ahead of an impossibly small time schedule and still deliver on all specifications, but only if he 'thought inside the box' (reminscent of another common phrase with an ancient heritage).
The key is that the physical description only restricts the base area and height and that the top room could be 'smallish'. The rest was easy.
Each report contained news of dizzying speed-to-construct, drastically reduced budgets, consistent design-specs-met, and galloping increases in stress-tests (mental breakdowns). All this from merely 'stepping in' toward the center with each row of bricks.
Voila! An impressive sight and shape from any distance, all constraints in line, and a three-foot-square mother-in-law room at the top!
As with many such innovations, the shape became a must for all that followed.