Comment by lukan

"Which means that either there is no such an internal pressure or the regimes are extraordinarily good at selecting and incentivizing people to maintain the status quo."

Or there is pressure and discontent, but simply not enough to topple the regime as it needs way more than 50% support for a internal regime change.

I have childhood memories of such a succesful change in eastern germany. Most people had enough for a long time, but they knew the sovjet tanks would come if they revolted. After it seemed the sovjets were busy on their own and won't come but rather did democratic reforms themself, but the GDR refused and stayed stalinistic - then the people went to the streets. And at some point those in power just gave up. Not really a consciouss choice, but they were visibly insecure and confused, so weak and fell. (But it was a close call, some wanted to bring out the machine guns as well)

The iranian mullahs were insecure, but they choose the violent path of dominance.

Not the same situation, as they did not rely on a foreign power like in GDR, but it seems they lost majority support a long time ago, but have a loyal enough religious base to use the weapons.

And yes, military and police who have family members on the streets will defect at some point and it seems that also happened in Iran, just not enough.