Heh, well, another lesson from chaos mathematics is that in iterative systems, you don't really get "explanations" the way we humans like to think of them... the answer to "what caused X" for any X than has taken a long time to develop is "everything". So rather than culture "or" social structure, I'd say "and", "and" also a lot of other things, and also the culture and social structure are themselves affected by the very personality structures we're trying to discuss.

Determining "causes" isn't as hopeless as that makes it initially sound, but you need something more sophisticated than the normal human concept of "cause" to even approximate useful answers. The good news is, this isn't impossible; we all live in an iterative world and we operate in it even so, which requires us to have certain models that conform to the world. It's one of those cases where I don't really love the "humans are just horribly irrational" gloss; our instincts and intuitions often have greater rationality than we realize, because they were formed in this iterative world, and sometimes it is in fact the particular naive concept of "rationality" we are trying to measure them by that is deficient, whereas if you use a more sophisticated one we look less bad.

(But sometimes humans just act suboptimally, no question about that.)

Another thing that helps is that you aren't generally interested in modelling the entire system. For considering myself and whether I may want to, as the article discusses, make changes in myself, I can take my culture and environment more-or-less as a given; I need some flex to consider options like "well what if I just up and moved to another country?", but I don't need to consider my own effects on society very much because they are some complex combination of "tiny" and "utterly unpredictable". While society is chaotic, the time frame of the impact on society from me changing from excessively introverted to somewhat less introverted is way, way past my horizon for making decisions.