Before the military dictatorship, there government was oligarchic. Their marriages are often marriages of convenience to tie politic factions together.
You actually have no idea what the form of government was before the military takeover. We DO know that 500 years prior, before the creation of the Union, that the Cardassians (probably called Hebitians then) were peaceful and very religious.
We may actually be looking at a more Bajor-like society pre-Union, and given that, all bets are off as to what their customs were before the military took over.
They were still an oligarchy even after the military coup. Just look at the family ties. Enabran Tain and Elim Garak, clearly power consolidated along family lines. I think there are a lot of examples, but I need to spend time seeking out the exact quotes. You know, the push toward oligarchy is present in every system, that's why the French guillotined their royalty. I can only say, until I find you better evidence, that whenever they talk about Cardassia society, it seems to be about powerful families.
So that's why family is so important to them. If you embarass the family, it affects their livelihood, and any future chance at power. And that's why they have so many secrets. That's why they share their secrets with their children when they die. If my family has a secret about your family, my son can hold it against your daughter and maintain the power for the next generation. They aren't seeking forgiveness with their deathbed confessions, they are consolidating power.
Unless I am misusing the word "oligarchy". Am I?