I don't think you can define how and why I place comments.
In general, I do not just leave comments on pieces I would like to own. Certainly those that match my tastes are more likely to get a comment.
I also leave a comment if I feel or learn that the piece is important to the owner, even if I think it is %$&^%*^
Finally many other factors determine whether or not I am more or less likely to leave a comment, such as:
1. I am more likely to comment on a friends piece (all things being equal)
2. If I am busy then I am less likely to leave a comment.
Malvin