Most spies and subversives of this sort do it for the thrill, and because they think they can get away with it. The "leverage" you describe is sometimes employed, but it's not usually the critical factor in their decision to do this kind of thing.
That's also why the money or other benefits involved often seems low for the acts committed.
I didn't. Anyone who gets any level of clearance (or it used to be this way) has to go through training and they go over all this stuff in it. They try to push the "leverage" narrative hard in them, but it's pretty clear what really motivates these people. They're generally either depressed (not enough thrill in their lives, spouse cheated on them, etc.), pissed (e.g. because the gov't did something they didn't like) or narcissists ("I'm better and smarter than everyone else, and I can get away with this"). Almost everything else about the motivations behind their actions is a distant second issue. They'd have done what they did whether the leverage existed or not (and it often doesn't).
That's also why the money or other benefits involved often seems low for the acts committed.