Spoilers for later seasons of DS9 below:
From the series I gather that Cardassian culture loves conversation and talking and that the government has been repressive for quite some time. We hear about some Cardassian literature through Garak, which of questionable quality according to Bashir. That may just be due to cultural tastes, but another option is that this government approved, published literature isn’t actually the best that Cardassia has to offer. Perhaps the best literature in Cardassian society is actually oral literature.
In ASIT, Garak infers that Cardassians have better memory recall abilties than humans, which would allow them to remember oral literature even better than humans. And we managed to create great works of art via oral literature - most famously Homer. Oral literature would exist in no physical form - there’d be no way for the Obsidian Order to punish you unless they heard you speak the story aloud. Otherwise it would stay safe within your head. It’s also my headcanon that the Order is a bit more lenient with oral than with written literature. Oral literature can’t be mass distributed as easily as the written word, and is therefore treated as slightly less subversive.
This means that Cardassian society is full of storytellers, telling tales from days gone by - all the way back to the Hebitian era. They tell stories that don’t quite conform to the strict edicts of the state - stories that occasionally make fun of the talking heads screens, of the endless trials with their foregone conclusions. Even dark subject matter such as the Obsidian Order and its torturers comes up occasionally - usually presented with a dark Cardassian sense of humor. The truly accurate version of current events and of the long history of their world is told not in the written annals, but in the voices and memories of the ordinary people of Cardassia.
And THIS makes the ending scene with Garak all the more poignant and heartbreaking. To lose 1 billion people (1/9th of the population of Prime according to a number I saw) is not only to lose scientific and artistic minds - it is to lose the stories, the histories carried in the minds of all the people. Whatever knowledge of Cardassia’s past they carried, whatever literature they knew is gone forever. When your cultures’ literature and history is all oral, to lose so much of the populace is an irreparable loss.
