Is that necessarily true? Likely we know much more about the most highly developed societies so that's where we would more likely discover ancient writing.
I'm saying the GP's claimed causal relationship between advanced civilization and writing might result from advancement causing more evidence to survive. Certainly there are undiscovered caches, of course.
Plenty of people lived in agricultural civilizations that were not the "most highly developed societies". Also, I'm not sure hunter-gatherers couldn't develop writing, though I know theories and could imagine reasons either way. How do you tell your compatriots, coming in the next few weeks, where the good food is?
You are still conflating 'advanced, settled Bronze-Age civilizations' with agriculture. Most agricultural communities were not 'advanced' (almost by definition).
> We have plenty of artifacts and paintings from hunter-gatherers
Though I'm not sure of the point in the parent comment, here's a story about how discovery of writing works:
Beowulf is the greatest discovery in the history of English. It's the earliest epic poem in any Germanic language, and by itself it is about 10% of known Old English poetry. The date of the story's creation is unknown, with estimates ranging from 6th-8th century CE. The manuscript we have today is thought to have been written (not printed, of course) in the south of England, maybe between the 10th and 12th centuries CE. And at some point after that, the story and manuscript were lost to time.
The physical document reappeared from oblivion, sometime before 1563 in the collection of Laurence Nowell. Nowell, unfortunately, didn't know (or didn't reveal) what they had. The document was there, but Beowulf the story and that manuscript were still lost.
And that continued to be the situation for over two hundred years, as the manuscript passed through at least two more hands, and still Beowulf was lost to time. In 1731 the manuscript was caught in a fire (!). Almost, it was forever consigned to oblivion before it was even discovered, but the fire only charred it around the edges, costing us a few words here and there, and drying the very old pages to make them even more fragile. Many other manuscripts were lost.
Finally, around 1790, Danish scholar Grimur Thorkelin read it and realized what he had. (Thorkelin then sat on it for another 25 years before finally publishing in 1815!)
Are there records we haven't discovered? Yes. Are they lost to history? Not yet.
