I didn't want for it to be a mandatory HMD, but really for there to be some more encouragement for people to respond to the HMD posts, or at least acknowledge to others that, no, they won't be posting to it.
It isn't even crit about activity, really. Even for people who have been on hiatus, I think it'd be beneficial to post to the HMD for characterization issues. People have posted to the HMD despite hiatuses in the past, and have made a note about it. Just look at the most recent HMD: almost everyone acknowledges the activity issue and, for that reason, seems the crit focused more on non-activity crit.
I just find it frustrating when there's no where to leave that crit. It's one thing to miss it one month while on hiatus, for example, but for a few months on end? And then to not have a post elsewhere for crit? It can be really off-putting.