History lesson time! This fascinating look at the history of video aspect ratio. Oddly, no one really knows why the 4:3 ratio was chosen but it became a standard just out of being commonly used. It would be an entire generation of movie going audiences before things began to change – and the wide screen wars began.
Probably the best wrinkle in aspect ratio history is how 16:9 came about: old 4:3 movie theaters birthed 4:3 television sets which stopped people from going to 4:3 movie theaters which made 4:3 movie theaters go widescreen to offer something different at home (which also eventually gave way to widescreen TVs).