Gaming is quickly becoming one of those things that people pay to see other people do, like sports or… acting. Imagine saying to the creators of Pong, "One day, folks from all across the world will tune in to see non-celebrities play video games, and not even play the game themselves." They'd probably have a hard time wrapping their heads around that.
But it makes sense that it would follow that trajectory. Some video games are so complicated and difficult these days that it's a genuine feat to accomplish them, so it's impressive to watch. The popularity of the commentary YouTube genre has also proven that it's fun to watch someone do/watch something just because they're funny or have a charming personality. So thus the immense popularity of Twitch streaming was born. And now we can even do one better-- look at memes about video games. Same thing… almost.