A natural spring in the desert that fountains water up 100+ meters, and they decide to put a huge pyramid-shaped stop on it, presumably to get rid of the luscious oasis that must have been there? And that fountain somehow, in thousands of years, didn't find a new way out through the limestone, which is water soluble?

I think it is more likely to claim there was an oil well there.

Edit: it wasn't a desert at the time they built the pyramids, but blocking a natural spring never was a good idea over there.