Note that the list of top-posters is fluctuating. For example I have been a top-poster only 3 or 4 times with long time inbetween. I think there are two populations: Some posters who contribute a lot - often in the form of comments. And then there are posters which are posting to Main and quickly rise to some prominent position in the top-posters due to the x10 karma.

My own scoring:

1) Make the world better (raising the sanity waterline etc) -> 5

2) Fun (spend my spare time here) -> 7

3) Friends (here because my Real-Life is here; and so I come to hang with my friends - or my internet friends hang out here) -> 1

4) Gather rationality (maybe you still gather rationality from LW; maybe you have gathered most of what you can and now are creating your own craft) -> 8

5) here for new ideas (LW being a good place to share new ideas) -> 8 (ideas new to me) 4 (genuinely new ideas)

6) here to advertise an idea (promoting a line of thinking from elsewhere - could be anything from; more Effective Altruism; to this book) -> 3

7) Here to create my own craft. (from the craft and the community) -> unsure

8) other? (as many other's as you like) -> learn about online socializing, forum contributing, writing