I tend to write as much as I can, but since HubPages are not the only place I write it seems like I don't have much hubs, while in fact I have hundreds.
I say you can't expect to have traffic and earn something unless you promote your articles, although I would love to simply write that is impossible. I have 4 or 5 bookmarking sites which I have invested time in. So I have plenty of followers there that read my updates all the time, digg, stumble upon, twitter, etc. While I have a profile in over 50 bookmarking sites.
I expect that the bookmarking sites I invested time to comment and reach out are giving me traffic, which they are, and I expect the rest to serve as backlinks that help me in the SEO way and also help me get each of my pages indexed in a matter of hours and also to get ranked well :)
You need to have both, if you are expecting to get your hubs read only by fellow hubbers than you can just write, but that will not make you money. In order to make money you need traffic from outside sources, so you must promote each and every hub, that is how it goes.