They make money through demographic targeted advertising. If you try out the process to set up an ad, you'll notice that, as an advertiser, you never receive anyone's personal information. That seems in keeping with the points above.
Most ads that you submit get rejected on sight, but if you post the same exacting thing at another type of day it gets through.
Mainly their ad platform is surviving because the sheer volume of impressions they can serve is hard to ignore. Other than that, they damn sure aren't making it easy for advertisers to give them money.