The fact remains that moderating forums is labor, and stack exchange receives a lot of value from that labor that the mods themselves don't see a dime of.
You have it wrong though: they get plenty of compensation through reputation, clout, and a feeling of power over their peers and being heard and helping out in a community that they love (or some combo of these). That's why they do it. Why is that not a fair trade without money exchanging hands?
Growing up, I used to mow an aging neighbor's lawn because he was basically couch-ridden. It made me feel good to help someone else out. Was I being exploited and should I have demanded payment, or was that just a fair trade that I volunteered for and could quit at any time?
Or look no further than HN. Participating on this forum writing content and enriching YC's coffers is "labor". And our compensation is procrastination and venting and feeling some satisfaction for scrawling our opinions online. If we didn't like that deal, we wouldn't be here.
This isn't the case with HN, where the main contribution of the forums to their business is mainly brand recognition.
There's no shortage of people who want to be rulers of a community. Of those, it is always hard to find the ones who are actually fit for that purpose.
That sounds a lot like the "social influencer" pitches to get free stuff in return for "exposure".
All I'm saying that the situation is still exploitation, no matter how you cut it. More and more businesses derive their main value from unpaid contributors, and it's something that should give us all pause.
This type of discussion usually comes up in the context of internship positions, where federally an unpaid internship must not displace employees and must provide no value to the employer.