Minor spoilers ahead for SA.
Another possible theory is the lifestyle of the Shin vs the Alethi. The Alethi have a very violent culture where the strongest man often is the most successful one- many of them are warriors, and Kal mentions someone who made their way up in society simply because they were a very large person who was good at fighting. They are often mentioned as tall and aggressive/warriors in the same sentence (I think). The Shin are very different, leading very peaceful lifestyles where the warriors are the lowliest of people and are not valued nearly as high as they are in the Alethi society. So a possibility could be that maybe natural selection had a factor in it, where smaller people like Cenn (a young, small boy on Kaladin’s squad in the very beginning of the series) and Tien are killed off quickly and the stronger and larger ones survive, while the warrior types in Shin are outcasts from society. This theory may be a bit faulty, however, as not everyone in the rest of Alethkar is a warrior, but it was the only thing that I could come up with at the moment. My first and favorite one was the lighter gravity one, but CrazyRioter got there first.