Yes, I also wrote about this here: Why Has the Value of Your Steem Upvote Risen 60% in a Week?.
The main reason is the 5 days of inactivity for most people, or at least, 5 days below full power. However, we are coming up to 7 days past the point at which most users regained their power, so if the reward pool should continue to grow then we may be looking at a more general drop in activity.
This may not be such a bad thing if the activity that has dropped off is that which HF20 targeted.