What is your source of this graph? It looks like something that was "drawn" with excel. I would disagree that the max block size would affect the amount that people are willing to pay for their TX to get confirmed.

You also need to remember that there is no "set" fee for a TX fee, but rather the fee is based on how big the TX is (among other things). Also there are many "free" TX that are confirmed in every block (or almost every block)