At the moment I can see 3 mods (including myself) and 6 members online (although I can actually see hidden members, whereas you normal members can't).
There is quite a high ratio of mods to members for these reasons:
1) When the forum would see two or three spambot attacks a day, until we upgraded board security we had to use a whack-a-mole style system to minimise damage, which while not a direct reason for people getting modded, was a large incentive.
2) This forum needs 3 mods, given it is arguably the most active forum on the board. At any given, at least one Misc mod will be online, due to the fact each of us covers are different timezone (I'm UK, RSW is US and Drago is Oz).
3) Mods are modded because they satisfy certain criteria: they are active, the forum needs an active mod (or in some cases another active mod) and they are a trusted, valued member who has proven themselves worthy of the responsibility. You can't expect to mod people when activity is high and then demod when they are not. Whereas being modded is seen as a reward for being a good contributor, being demodded is seen as a punishment, and the member who is demodded would most likely leave the board (unless they were demodded by request or due to a long stint of inactivity). The quickest way to see a whole bunch of our most valued members walk out of the door is to demod them.
4) Some forums have a lot of mods because they have a lot of admin work. Fanfic has 4 mods and can justify that because they run several activities such as awards, competitions, newsletters etc. Likewise, RPG has some behind-the-scenes work that requires 3 mods and ASB ought to have more than 1 mod, given how intensive the work is.
5) This board has several forums that see little to no activity whatsoever, however, they still need to be modded, just in case they do see any activity, or if a spambot attacks their forum.