In the context for this post, there is no comparable hiring process or trust factor. There is a certain level of aptitude and physical fitness required, but this job is plain and simple military service with some extra schooling on top (e.g. foreign language, parachuting, etc.)

Manipulation and influence can look very similar, and naturally skilled manipulators tend to go elsewhere (I think there's enough research about career preference and correlation of "dark triad" traits to substantiate this).

In my experience, most of the enlisted folks doing PsyOp had little idea of what it truly involved when they first began; however, the Army remains eager to redirect the passion of 20 year olds into counterinsurgency / foreign policy tactics.

I'd imagine the main motivations are similar to those of spies: ego, revenge, money and ideology.

Hard disagree here, as this job is for enlisted soldiers. Ego and money are out on that alone. Revenge, maybe? But you really don't know where you'll deploy. Ideology... maybe as well? The Army understandably does a pretty good job of obtaining uniformity there.

Virtually all of the motivations of folks I knew could be abstracted to "things are truly bad for these people; how can we fix it?".

I think you're right