[tirrellp]

It was explained to me using the analogy of watching sports: One of the most entertaining activities for a human is to watch other humans do things. This is why professional sports leagues exist. This is also why “Watching people play computer games” is a perfectly reasonable entertainment option, despite it not being your preference.

[WheelsAtLarge]

I read some research that when watching sports the avid spectators at times feel like they are actually playing the game. So, for a small amount of time they feel like they can score and play like the professionals. In some ways they become one with the players in their minds. I suspect that's why we hear things like, "we won", "we scored", "we beat them." When in reality the fans had little to do with the action and the game.

There's also the simple entertainment of the game. The game can be thought of as a story that has a beginning, middle and an end that can be happy, exciting or just plain boring. It can also be tragic if things don't go according to the fan's expectations.

I think all of this carries over to why people like to watch streaming games.