Why are most commuter bikes OLD?

My wife asked me this a couple of nights ago as I maintained my 1986 Specialized Rockhopper commuter.
I told her I think it is because old bikes are lower theft risk and most commuters get parked outside all day.
In addition, They just don't make 'em like they used to! Any bike that has already survived 20 years is obviously low maintenance and that is what a commuter needs in a bike that gets ridden almost every day.