A:On the level of conscious and rational thought I find incentive in that the more questions I answer the greater probability somebody to look at my profile and then take a look at the questions I asked and possibly give a reply to some of them.
On the level of unconscious thought I would speculate it's a mix of the human need to communicate with other humans, the possibility to express one's own opinion on an issue and the associated illusion of exerting some influence on other people's thoughts and feelings on that issue; the possibility to fulfil one's need of emotions - reading opinions opposing your own or watching your "thumb rating" go up or down or the surprise at the discovery of new information on a topic you are interested in; the pleasant feeling of being useful, of receiving recognition through those thumbs up or a thankful note.
You can try posting an additional question "Why do people enjoy giving advice so much that they are always ready to give plenty of it for free?" and see if it brings good insights into this one.
