I suppose the pervasive stuff like vanity, the strong focus on pop culture to derive values, greed, and the tendency to imagine our own private fantasies as reality might offer some resistance to the practice of stoicism in the U.S… so maybe it’s less common here.
Perhaps a survey might be started on the subject among the atheists here at some point as a gauge. From what I can tell, a high percentage of the regulars are living in the Global North. I could be wrong about that.