Do you remember the late 70's? I remember driving home from work listening to the radio and hearing DOW trading volumes in the 20 to 30 million range and sometimes even less.
Remember, back then stock trading was done by hand and very slow (by 2015 standards) mainframe computers. That’s why 30 million shares traded was a lot in those days. Today, billions of shares get traded in a matter of seconds, thanks to modern supercomputers and much faster computer networks (much of it not connected to the public Internet).