Keep in mind that most people are in this for the money, and anyone's motivation is fine because everyone has their own unique ways of interacting with the world. I mean, I believe the world has the wrong motivations to do things, but everyone has the freedom to choose them (or the motivations choose them, like in this case haha)

Another thing you need to consider is that there are more promote-your-posts, receive-an-upvote, check-other's-posts servers.. So, basically, what I think you must do is think out-of-the-box. This is a little easier if you have a specific audience for your server, as in videogaming for example. It's easier to give game-related motivation to people, because you know for example, that many people would be interested in say, you made up some form of contest based on gaming or anime/comics or similar, or gave out prizes in some way with some of your cards for example. So it's a little more difficult to make up contests for a larger audience, so that they could al be interested.

That being said, it's not impossible to attract many people into staying active in the channel.