It's definitely not the lack of trading that's causing this. It's funny that you would even think that haha.
My guess is that the reason we see the horizontal lines is because let's say someone places a large sell order (say 1000 Bitcoins) at $11600. It takes a few minutes for the market to absorb it. The price stays flat until the entire order is bought.
I have had bitcoin since early on so I am aware of increased trading volume.
Thanks for the explanation.