Here is a really great video that goes over the history https://www.youtube.com/watch?v=7yRGvMgieEU Sometimes we think about the technical reasons and forget of the human and the developmental process that can sometimes have an effect on how things are today. spoiler for the video - its because too many 110v light bulbs were already in place by the time 220v ones were made and it was too expensive/difficult to change. kind of reminds me of why the US never switched to metric.