I think the main reason why you haven't seen it yet is the fact that bitcoin is still going strong. Since, bitcoin is making people money and helping them get profit people are putting their fiat currency into bitcoin as well as their altcoins to bitcoin as well. Which means as long as bitcoin keeps making people more and more profits than there would be nobody looking at bitcoin neither.

However, at the same time know as a fact that as soon as bitcoin doesn't make anyone that much money and the amount of profits are diminishing then the price of altcoins will start to go up because people love to make money and they just made money from bitcoin so they will not say "this is enough" and move on, they will want to keep making more profits and just spend all of that bitcoin profits into getting some altcoins.