I don't have a problem if people don't read or leave feedback. I just figure that people "do whatever" for whatever reasons they do. I think if you enjoy reading and commenting on their Hubs - then why not. If it's kind of a chore, and you're just doing it because you've been trying to support other Hubbers, maybe you should cut back on whoever/whatever would make sense to you.
I follow a lot of people and can only read the Hubs of theirs that catch my eye. (I also read Hubs that catch my eye but aren't written by people I follow.) One thing I know is that a lot of people don't want to leave "any old comment" on a Hub (especially now, with the quality of comments being "measured"). I don't know... People just do what they think is right, and a lot of people want to feel like they have something to add to the discussion before commenting. Sometimes a Hub "says it all" very well, and if nobody disagrees it with it, there's not a lot of people feeling the need to comment.
One thing I've seen people do is leave a line of text at the end of the Hub that invites comments/feedback. (I, on the other hand, shut off most of my comment boxes (LOL). As much as I appreciate comments (and I really do), I don't want to keep re-visiting stuff I wrote three years ago. :)