Hermes, I don’t think there is any such inability in Stoicism. Happiness is simply not the Stoic’s concern. None of the Hellenistic schools did. They were concerned with eudaimonia, the life worth living. As I mentioned before, it’s probably best to stay away altogether from the term happiness, because it is too vague, and means contrasting things to people.
We, or many of us, may be hedonists, but the Stoics challenge that that’s a good thing. And so did all the other schools, except the Cyrenaics, who embraced hedonism. One can disagree with that stance, but their arguments were pretty sophisticated, and they are partially confirmed by modern psychology. A focus on pleasure, material possessions, etc., does not actually make for a “happy” (meaningful) life.
I hear about politics, and I don’t know you, so I can’t comment on whether you do what you do for egotistical reasons. Somehow I doubt it. There are more lucrative ways to feed one’s egotism than trying to be helpful to others.