People often ask why revolts aren't more common, but its pretty easy to ask why if you've never taken part in one, you know "from the outside." Inside of a conspiracy the leaders, often, are chocked with fear, and mistrust: the leadership itself fraught with paranoia, while the underlings are given very little info. This is because of the dangers of such things.
To give a better more tangible answer to those who can't place yourself in said situation, like myself, ( I loved roll playing as a Dark Brotherhood member in elder scroll games cause it felt exciting ) use a surprise party as an example. Once you know it's going on you change, and you know you've changed, but you don't know by how much. You measure every interaction with a laser like focus you didn't know you could muster. You struggle to NOT mention it. You struggle just to "act casual." The leaders of said party are giddy and far happier than normal because this is a levity based thing, but to the person who ruins the surprise ... you will never, ever, EVER, hear the end of it. This is because it was taken with a true measure of care, and you ruined the plan. This carries over but with way more emotional depth to a life threatening situation.
Transfer this to something as serious as a military coupe and you've open a literal can of saran gas .... maybe on the ones you love.
First off how do you approach this conversation? "HEY BUDDY O' MINE?" No, because generals are often not friendly in the normal civilian way with each other, and because each military is different, this culture also impacts such things; and even if you are, this isn't something you "just bring up." The United States of America was a desperate creation made by men who knew there could be turncoats, but had the good fortune of finding themselves in a time when there was a lack of advanced technology (listening devices and such) and public outcry in town halls was still a thing. They could look to someone else pissed off about raised taxes, and find a likely ally, but in the modern age "how can I trust someone else so easily" is a thought anyone in real power has. Not to mention if a general in North Korea even talks about anything against (I believe it's called) "the glorious leader" (what a name

) than they quickly are put to death. It's so bad that if you, as a general, some how single handedly saved the country several times, just making a joke about it means you and everyone you love dies, often in painful scary ways.
But even if you doubt they do it this ask yourself why wouldn't this be the case for you if you ruled? We all like to be "peaches and cream" at the thought of leadership but look to the real world and you'll find out quickly you can't just be a fluffy person, and also be in charge. Mind you, I'm not saying you have to be rough person slap everyone just cause person, but you can't let talks of rebelling just fly flagrantly in your face. If you want tangible examples you can look up how companies against unions in the United States handle talks about forming one. They do whatever they can to put them down and this is just over small monetary power in comparison to something like a nation. You can do the thought experiment and easily see if they are willing to do that than of course a nation, a small one at that, is going to be even harsher: especially one who's leadership is, frankly, full of megalomaniacs.
Which brings me to your question about happiness; because, sadly, even beaten dogs will feel good over their abuser petting them, and this is the same for people. You might ask why and how, but it doesn't matter because this is simply something that exists in nature. There are levels to rebellion within someone and how much your willing to rebel is measured by that, but even than, there is also real world factors. If you show unhappiness it spreads "dissent in the ranks" and such things can never stand. This is why everyone is always smiling, it proves "that everyone is happy" when in truth it proves the opposite to the thinking person, but that isn't what they care about because it's about appearance. You can also see this in how they talk about themselves.
In a bar the guy bragging isn't the tough guy, the tough guy is the quite one who is self confident. The one who will actually not hold back if he needs too because, just like with a really large animal, they don't roar just to be heard: the small ones do that to appear larger then they are. In this you can see North Korea is full of insecurities. Look how our leadership handles things and how "easy going" they are when if anyone took a moment to think any one of them could easily bring about a death ritual to end a single person. It wouldn't be hard but they've never even once said such things because they're actual leaders. They don't sit around and show off their feathers nonstop to look intimidating, so if they who hold actual power don't, you can easily look to the stunted fools over how they are and know that it is because they don't have much of anything. Whatever small minded fool sits in office (something Jong) in North Korea now is no more than an evil creature, but the sad fact is they HAVE to stay in power. If they got replaced or did something on the world stage that looked like they wanted to change, they themselves would be killed. The whole of the world is controlled by a few large players who use the rest as cover for what they want to do. It's all just a game of chess, and in many ways I think this is another reason they call it the game of kings.