I think a number of things come into it. When I first started on Hubpage writing I posted only a few Hubs, maybe less than a dozen. Not much activity resulted. Then I really got into it, wrote quite a few. Got some responses, but not that much. Then I was advised to 'get involved.' This meant reading other people's Hubs, commenting on them. Becoming a follower of some of them. Emailing and communicating. Also, getting into the Forums and asking and answering questions.
With this action behind me my rating jumped from around 75 to 93. It dropped back, of course. But if you want followers you do need to post stuff they'd like to look at: well written, interesting subject matter, and some good pictures.