Sounds like they gave value but got none to me..."visibility" ain't worth shit. How much SO got in the bank? What's the ratio of visibility to dollars here? I've never seen an SO badge anywhere and never mentioned in any resume.
I suppose if your profile on StackOverflow is high enough you could put it on your cv.
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)
I would totally agree with that, however I have over the years developed the suspicion that people who make hiring decisions might not be operating at the same logical level that I am.
Given both that suspicion, and how they seem to behave about prominent github profiles and such, I think that being in the top 20th percentile or so on SO and a strong focus on the tags that correlate to the terms in a job announcement might be a big draw to some HR people/managers who just really don't want to mess up one more time! After the fifth complaint or so of programmers we hire don't know how to code or whatever - it might be soothing.
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