Most Helpful Girl
Well that's sort of like asking what the fun in watching sports is? Wouldn't you rather be playing football over watching it?
There are many different answers to this. Some people do enjoy the amount of skill and hard work it takes to master a video game, and they find it just as exciting as watching a game of hockey or football. Other people find the commentary enjoying, as well as the personality of the player, which might give more depth to the game. I belong in the latter category. I like story-heavy games, so it's kinda like watching a movie, and I'm very picky about who I want to watch. I prefer players who are calm, who don't scream/shout at the game, who pay attention to the small details and who have insightful commentary about the game.
Most Helpful Guy
The best way to think about it is like watching sports or watching a cooking show. Like those, you would get more enjoyment doing the activity yourself, you still get enjoyment from watching it be done with the added enjoyment of commentary. In this case, usually comedic. Another similarity is accessibility to resources. If you want to cook something you see on tv like a cheesecake, you might not be able to get one to all the ingredients or a spring form pan. In gaming, you might not be able to pay for an expensive game or the hardware needed to run it.