People unfollow for a variety of reasons.
.1. They don't have enough time to follow, read hubs and comment.
2. There is not enough activity from those they follow ( commenting, interest. )
3. They may be cutting back on their list for a period of time. ( To write more hubs, etc. )
4. A low hub score from the person they follow.
It can even be personal problems which have nothing to do with you.
But I can guarantee you that if you are consistent with your comments you will not see an "unfollow" unless the person is leaving hubpages. And the more detailed your comments are, the longer your followers will stay with you. A comment such as "great hub" is too generic and doesn't show that you have read and learned anything.
I am consistent about revising my hubs too which keeps the content up-to-date and fresh. I spend time on older hubs adding better quality photos and videos. I even update the amazon capsules.
In my soon to be 3 yrs on hubpages, I have not had 1 unfollow (that I know of). :)
I like your question. Hope I have helped in some way.