I don't want to speak for Chopper as I'm sure he'll weigh in, but he does seem to indicate that they are overwhelmed with flags from time to time.
I just went over our mod list, and I notice that many of our mods are only doing flagwork or commenting on things that might have been flagged - not answering questions. One mod (Karfa) is very inactive.
They aren't just called "Moderators", they're called "Community Moderators" because they're supposed to actively participate in the community. The mods in my timezone-range for moderation (EST), from what I can tell are: Kara Marfia, Mr Denny, and Sysadmin. Mr Denny actively answers questions, but I rarely see him on m.sf and I never see him in chat. That's almost a week. Sysadmin still actively answers, actively participates in m.sf, and is in chat from time to time. I never see Kara do anything. Ever.
For mods outside of my time zone, Chopper is always in chat. Always answers questions, and always participates on meta. He's incredibly active and I see him more than I see any other diamond, and he's on a 5 hour offset from me. I hardly see Sam, but he's also halfway across the globe, so I can't speak to his activity other than there isn't much on m.sf. The same is true for splattne. Italy is far away, he could be very active while I'm asleep, but I don't see him participating in m.sf. Mark H is also halfway across the world, but I see much more activity from him.
I don't want this to seem like I'm calling anyone out, but it seems like someone needs to put the "Community" back in "Community Moderators". The positions were originally created so that highly respected members of the site could help run it. It is becoming apparent that this just isn't the case in some instances. If this is because they don't have time to participate because there aren't enough mods, then we need to add more mods. If it is because some people have just become inactive, then they need to be removed from their positions and replaced in another election.