Moderators are busy.
They try to handle a lot of work on Stack Overflow. I see that the flag queue is pretty full most of the time and I for instance have 2 mod-only flags being active for a week now. I am not the only one with this problem. No real problem there - it seems to work out.
But I ask myself: Why don't we have more moderators?
It's not like they get paid. And I am sure there are capable people out there ready for the responsibility. And when the work of moderators would get easier and a little less - nobody would get hurt. The time to instruct a moderator pays off multiple times. Most moderators keep up their work a long time.