I agree that there's all kinds of reasons people don't feedback, and I'll add another--not getting a response from the author. I really hate that. If I leave fb, I want the author to say, Thanks. I don't expect anything more than that, especially if it's a highly trafficked fic, but I do expect that. I make exceptions for fic with hundreds of comments. I know I couldn't answer all that fb and don't expect someone else to. It's just good manners to say thank you when someone says something nice to you. I know a lot of writers get tetchy when people suggest that a response to fb is a good thing, but I can't help it. I'm Southern.