It's hard to answer this question because you don't define substantial traffic. But I think a lot of it has to do with the experience of the Hubber. New Hubbers, who have never written online content before, have a lot to learn. New Hubbers, who are experienced with online writing, will know more right away and probably get more traffic. However, every platform is different and it takes different skills to monetize them effectively.
Paul Edmondson once said that it took a few years for Hubs to reach their full potential. However he recently amended that statement saying hubs might mature more quickly in this post- Panda and Penguin world.
It also depends on the stability of the HubPages platform. Recently there have been so many changes, it's hard for a new Hubber to see what works well for them.
For me, I had tried several topics and formats and thought I knew what might be working well. But then the patterns changed. I don't know if it was Google, HP or the time of year.
I've only got 27 hubs so that's not very much to make a judgement from.