One thing I don't see the article mentioning is how rigid Egyptian culture and society was from 3000 BC up to the time of Alexander the Great.
The Narmer palette is the classic example of how the artistic style sprung up almost fully formed in just a few hundred years. After that, it all was just minor variations on the same theme.
It's similar to how many modern banks or courthouses have greek columns: when there is cultural continuity, some styles just live on after they reached maturity until the entire culture is wiped out.