I did a little checking and there is suprisingly little agreement about the span of time between Zoser and Khufu. The last site I saw said about 150 years but I won't quibble. Let's say two hundred years which gives you 2 x hundreds. Close enough for government work even in Egyptian times.
There is still a magnitude of scale between the size of both Zoser's tomb and Sneferu's tombs and the Giza Pyramids (except for the 3'd one) as well as an apparent discrepancy between the size of the individual stones used in construction.
But let's forget all that for the moment shall we and purely for the sake of argument let's accept your premise that this culture retained all the knowledge from its past and built on it.
We have the Step Pyramid (primitive compared to the GP) and Sneferu's Red Pyramid and Bent Pyramid ( which could have been designed by FEMA in modern times) and then the Meidun thing which may or may not be his. From there, almost by magic, the Egyptians produce three perfect pyramids two of which are on a scale which still boggles the mind (and, in all honesty, tempts people to speculate on how the hell they did it.)
Then comes the 5th Dynasty.
Userkaf
This ruined pile lifes to the northeast of the Step Pyramid and it little more than a pile of stone. We snapped this picture while walking to the complex of Saqqara.
However, it is a fairly important monument, marking the return of the pharaohs to Saqqara as a burial place. Userkaf, the first king of the fifth dynasty, built his pyramid here close to the step pyramid. In fact, it is exactly located at the northeast corner of the complex of Djoser.
This was a small pyramid to begin with, and it has collapsed even more with the inevitable plundering of its fine limestone casing. The interior blocks are left in a rough pile, and appear to be uneven, thin slabs of limestone stacked into roughly pyramidal shape.
Sahure:
Neferirkara:
(Almost looks like they were reverting to a Step Pyramid there, doesn't it?)
Niuserre:
Niuserre's pyramid is in no better repair than the others at Abu Sir. It is swashed into the space between Sahure's Pyramid and Neferirkare's Pyramid, even to the point that the temple and portico are a strange l-shape, to avoid mastabas that were in place, and to allow NIuserre to usurp the valley temple foundations of this father, Neferefre. The causeway is the most complete on the site, however.
Apparently, they couldn't get a better shot of this one because the area is now a military reservation or something.
Neferefre:
Menkaukor
There is that damned step pyramid 'echo' again!
Djedkare:
and, last but not least...
Unas:
Now, it could just be my imagination but it sure as hell looks as if the Egyptians lost the secret for building pyramids as quickly as they learned it.
In fact, and this is not my observation, I read it somewhere but I certainly agree with it. Judging by the remains it seems fair to draw this analogy. Egyptian pyramid-building artistry seems to have gone from producing a Ford Model A (Zoser) to a Ford Model T (Sneferu) to a Ferrari 360 Modena (Giza) and then reverted to horse and buggy, (the 5th Dynasty wrecks.)
I am sure as I'm sitting here that the Egyptology Club has a simple answer for this apparent disparity...but you know what H.L. Mencken said about simple answers.
Something is wrong here. War, disease, death, destruction, hunger, filth, poverty, torture, crime, corruption, and the Ice Capades. Something is definitely wrong. This is not good work. If this is the best God can do, I am not impressed.
-- George Carlin