While the purchasing power is important, to some advertisers, eyeballs is enough. They know eyeballs eventually convert, even if you have to retarget those eyeballs nonstop elsewhere (pretty sure they can be followed elsewhere). If you know this, you pretty much have an untapped source that few will try to replicate because of the first barrier exhaustion.
If you can garner attention on there, you can extend any noteriety elsewhere that converts better, or can be leveraged into getting in front of those converting folks.
