I can't speak for Whitney, but I know why I've disabled most comment capsules (except for the latest Hubs and a few that have comments that contain useful/helpful information to anyone reading SOME Hubs). I wrote a whole Hub about my own reasons. ("Disabled Comment Capsules on Hubs")
My shorter reason is that I don't want to leave comments unmoderated (because who knows who will put what questionable links in as comments..), and I have some Hubs that are from - like - 2007/2008. I'm really not able (time-wise) to keep going back and replying to comments on Hubs I wrote years ago. Some of them were written in reply to requests about serious subjects (like "moving on after losing someone"), and at the time I wrote them because I thought the person making the request deserved as serious answer. They're depressing, though - especially when I wrote them, want to now just leave them, and was getting serious comments on them that required serious, thoughtful, replies whenever they'd show up out of the blue. I've always very much appreciated comments, but it was getting to be a part-time job to give a lot of them the attention/reply they deserved. So, I decided to risk sacrificing traffic and disable a lot of the comment boxes.
I know that sounds like, "I'm too busy to be bothered," and it really isn't that. It's more that I have some challenges in keeping myself in a positive, moving-forward, frame-of-mind; so feeling as if I was always being "called back: and "pulled back" to the past wasn't just a matter of time. It was a matter of my own needing to feel that I am in in the present and moving forward - not always being pulled backward. :/