what we can do to encourage more participation in commenting
The only possible way to fix that would be to not hold the fest when every other fest is going on at the same time. ;) I had to fold weeks ago due to sheer volume of reading material, not to mention having prompts of my own with deadlines to work on. It'll be ages before I get through reading and commenting on everything that takes my fancy, and it's most assuredly no one's fault, just a lack of time (and a bit of an overdose).