Regardless of who this question was initially directed at, I'll answer it anyway. In the beginning, I found HP after getting tired of the limited space on FB and the lack of any real feedback one gets through Blogger.com or other venues.
I joined HP and then got seriously stuck for something to write about. I wanted something. Some topic. So I just let it ride for a bit, but during that time, I received emails from some asking the same question. "Why don't you have any hubs?"
Today, after almost a year, I still only have 48 or so but I just write when a vision hits me for a specific topic. Could be some are in the same boat. They join and then come bak after a while and write something.