White rice has few nutrients compared to brown rice and it requires more processing to make. If you're poor and hungry then brown rice seems like an obvious choice. What's the story with the switch to white rice from whole grain rice?
The answer is not in history, but in food science.
White rice can be stored for decades. Brown rice normally can barely be stored a year.
Since no one knew any nutritional data, they naturally preferred the stuff that kept better so they could store surpluses against future bad harvests. Brown rice also takes longer to cook, requiring more water and firewood. White rice is the obvious choice, if you can get it. The poor often wound up eating millet, barley, sorghum, or other grains, not rice at all.