|The Drunken Dragon|
I do agree that Golarion's timeline as a whole does appear to be a bit odd, given how magic should have sped up technological innovation rather than slow it down (mainly because it reduces certain limitations that humanity had to abide by for so long, thus resulting in the fits and starts of development mentioned by other posters). The only potential reason why nobody has used magic to kick-start advancement is because of social suppression. But that's actually quite unlikely, as many of the cultures listed on Golarion have cultures that focus on equitable distribution of resources, or are wealthy enough to try (like some parts of the main Keleshite empire). In a world where instantaneous communication, fine-tuned perceptions of reality, and access to the minds and observations of beings literally present when the universe began, science should have exploded loooooooong before Golarion hit the 4000's mark post-Aroden. Heck, the Azlanti had interstellar travel and their history (while the length is rather obscure) is implied to be somewhat shorter than the modern period. The fact that Numeria exists, Technic League not-withstanding, means that somebody might have been able to, if not reverse engineer, than at least finagle understanding of complex mathematics and engineering.
Nidal, comparatively, is incredibly easy to understand. Their cultural stasis is mandated and upheld by a divine being. In a world where magic exists, and the populace willingly signed their entire country away to a god, that makes sense.