For me there are three reasons. The first is to see if a game is any good. I'll check out some footage and if it looks fun I'll stop watching and buy it. The second reason is the player. Some have good commentary,others are so pro its amazing, and others are so terrible its hilarious. The third reason is its fun. I've watched my siblings play games (and played with them) for years, so I guess its only natural for me to enjoy watching other people play games.