Missing fossil fuels are one way to explain it; another is intentional technological stagnation/regression (see David Weber's Safehold series). Yet another is a metal-poor planet. Most of the inventions which have advanced us by leaps and bounds were invented using or because of metals.
Edit: One more possible explanation is recent colonization/terraforming. You started the "clock" at egypt, but evidence suggests that we were around for thousands of years before that, stuck in a hunter/gatherer mode and not advancing at all.