Earlier quoted context omitted.
They've got compensated in visibility. I don't know any moderator with less than 20k points to date. And the more points you have, the upper you stay in the ranks and you can always embed their badge in your website. So, yes, they don't earn money, but they receive visibility
What does this visibility mean? Can it be converted to cash somehow?
SO also has a jobs site, which I suppose can be linked to your profile if you want it to.
A company I consulted at one time was trying to improve it's profile for job applicants so they wanted people to put up their github profiles and SO profiles in some advertisements or whatever they were doing - I think it was on linkedIn they were doing this. Anyway I think they stopped because nobody had a particularly high impressive number so why would you even want to do that (but they did it)