I have tried a few out and here are my reasons for not staying.
1. The site is not monitored properly and people are allowed to do what they want including using other people's work.
2. The material you write does not belong to you. (yes this happens)
3. The people are not friendly
What keeps me here at hubpages so far?
1. The people are friendly
2. HubPages does a great job of monitoring this site for duplication and overly promotional hubs (I know, I've had both happen to me)
3. The hubs I write belong to me.