Some don't, some do.
A lot of people would just follow BTC without bitcointalk.
Once you see an advantage of posting in something that already interests you, you get deeper into it and create content that might be useful for other people later on (and they'll find your experience online).
I think that's just wrong. I don't mind people getting a bonus for something they would do anyway, however if someone is basing their contribution to the forum on getting paid then I'd prefer they wouldn't post at all.