When I was streaming, I would get my best viewer counts from a couple of sources:
1. When I casted TF2 matches
2. Doing stuff in Kerbal Space Program on a regular basis
I'll take these in reverse order, when it comes to streaming, it's good to stream consistently on a regular schedule and have a consistent schedule of when you stream. For a bit I experimented with doing daily KSP streams for a couple of hours and do a variety of informal segments, usually involving doing some mission to the Mun for specific purposes (since it's easy to fit an entire mission there and back in a couple of hours). Then close to the end of the stream I would do silly stuff around the main base like attaching rockets to trucks and flinging them down the runway. I think I did this for about 3-4 weeks and at the end was able to consistently pull about 15-20 viewers, usually the second or third-best performing KSP stream whenever big names like Ridgedog weren't streaming as well. Mind you I'm no KSP expert, but at any particular point I'd try to explain what was going on and what was going to happen next (rapid unplanned disassembling not included).
Now to TF2. Typically when I did casual pub/pug streams I'd only get 5-7 viewers, but then I started to cast lower-level matches and slowly I was drawing more viewers. I think my peak was something in the neighborhood of 50 viewers casting an IM playoff game while TFtv was on as well. I'm not exactly the greatest at much of anything TF2-related, and I had a few glitches during my casts, but I tried my best to tell the story as it happened and got lucky with a few close games that other people didn't cover.
So, I think where the link is missing for TF2 is this: Viewers want to watch either really good players playing, or want to watch really good games at a decent level. What they don't want to watch is stuff they could easily do themselves.
That's just my observation, anyway.