I asked about this in the forums. Apparently, it takes some time before you'll be seeing search term results. Those search terms are what people type into Google and how they find your hub. And the search terms are also connected to what you'll be seeing in the Title Tuner.
Before, all my hubs didn't have the search term data and I don't get any suggestions from the Title Tuner. But now, some of my hubs already have search terms and I'm seeing some suggestions in the Title Tuner. So it just takes time for you to start seeing all this data.