It's one of the contexts in which I'm willing to be the change I want to see.
It's disappointing to click on the comments for a post and no one (especially the submitter) has told me what I'll learn/experience. And yet, there it was, four hours old, ten points up and no comments. So I give it a skim and it's really good. Now I want others to read it. Spending five or so minutes polishing three sentences is basically free for me and positive sum (unless I do a bad job).
Cynically, tl;dr submission summaries are how I've chosen to feed the beast until it grants me downvoting power.
Also, thanks.