Is the reason to restart with fewer players because the number of players (and factions) you have is to high, or is it because not enough of the signed up players are participating regularly?
If there's just too much going in too many directions, I urge you to change whatever you need to change to make sure that the game stays fun and manageable for you - your plan to reduce the factions makes sense if that's your reasoning.
If you are concerned that too few players from most of the factions are being active, but you yourself are not having any problems with the time it takes to run each faction, I would ask you to consider continuing the game as is. My reasoning is that I believe that most players who are active do want to play as they have been - guys chime in if I'm wrong. I think the active military players are quite happy being military, and the survivors are quite happy being survivors - after all, the only faction you urged people to take so the game could start was actually the Utopian one!
There's 10 of us Utopians, but 5 are actually NPCs. I urge you to treat anyone who doesn't give an action within a reasonable amount of time as an NPC, at least for that turn. Have them continue as they are. Describe them as seeming depressed and uncommunicative. Maybe they're coming down with a cold or something, and have them do basic obvious reasonable-to-the-situation things...
Or if you really don't want to run PCs-as-NPCs, warn us that inactive PCs will be carried for a max of X turns, then the character will decide to kill itself, so players need to stay active or else.
We do have a small influx of joiners - players who've waited days, and in one case, weeks now to join their faction.
To my eyes, none of these factions are boring. Each is different, yeah. But any and all of our factions could end up doing some surprising and enjoyable stuff. Thanks for keeping the game going, I know I am quite interested in seeing how its future plays out, regardless of whether you do restart us or not!