Yup, this place is starting to gather cobwebs. I think there are a lot of factors. Back when Escape Pod started, over 10 years ago, the social internet was a very different place. Specifically, there wasn't nearly as much of it. Now you have a lot more facebook, a lot more twitter, a lot more demands on your internet time. Escape Artists are using those mediums too - particularly twitter, where we post about episodes and people do respond and comment quite a bit - though not in at the depth we often see in the forums. I don't think a lot of twitter users are bothering to come out here and add another site to their routine.
Also, just from my personal experience, a lot of my friends have reached social networking overload, and have turned their back on it entirely. Deleted their facebook, gotten off twitter, and things like online forums are going to go down with them as people adjust their lives to focus on in-person interactions.