It always blew people's minds when I told them that 50% of the engineering time at reddit was spent on moderating. What's interesting though is that we didn't even have any moderation for the first year or so, because the community would just downvote spam. It wasn't until we got vaguely popular that suddenly we were completely overwhelmed with spam and had to do something about it.
At some point the engineering work can be something approximating “done” (or should get asymptotically close to it), and the health of your platform ultimately rests a lot more on the quality of the community than on any particular technical project.
What is engineering doing that it takes up as much person-hours as moderation? Running A/B tests to tweak the “try the app” dialog?
(Yes, I’m bitter… I deleted my Reddit account years ago and I’m still lamenting the loss of what the site used to be.)