Every viewer will be different. Personally I am watching Terraria streams at the moment. A streamer could impact a change to their already existing followers by changing the game for a day. Some viewers might want to try that game out. Now, there is another way a streamer could attract viewers, and that would be going for the trends. A random game blows up and people want to either try it or see how it is first. Some of your viewers will come to watch and maybe some new viewers will come.