So it took 12,000 years of human settlements before we developed writing? Even though there was rudimentary writing in caves.
There must be some evidence of the starts & stops of writing among the earliest civilizations [or should I say settlements]. Perhaps it is writing itself that delineates the difference between a settlement and a civilization.
Writing requires settled living. Settled living took off best in the riverine cultures, which were based on settled agriculture and animal husbandry, and those activities required land, and property rights had to be recorded somehow. Accounting began first (in Sumer, by 3500 BC), and that led to writing.
Walled towns are at least as old as Catalhoyuk (in modern Turkey) and that town lasted over 2000 years with no streets -- residents walked across the roofs. Obviously they had food storage, animal bones have been excevated in plenty, and just as obviously they must have relied on farming and herding as well as their location on the obsidian trade route.
The pattern in Sumer was to wall the main town, work the other territory, go home at night, and a central authority maintained a standing army for common defense. There's no good reason to believe that the Catalhoyuk-ians didn't follow that pattern, they're just not (yet) known to have had writing.
Another impediment is, writing probably relied on perishable materials, much as it does now, and between obsolescence of the data due to age (language goes extinct, a relatively small literate class dies in an epidemic or meets, say, Mohammed), and the occasional arrival of a successful band of reavers (sometimes from the none-too-neighborly neighbors), those will vanish.
It's probable that there was some combination of independent invention and a now-lost chain of development and inheritance (as was the case with cuneiform, but not so much with Egyptian hieroglyphs) and not just in one region. :^)