Poker players love online tournaments because there are chances to earn big amounts with relative low investment. 
The spectators love to see these players battling it out, because the game is more based on skill.. and not so much on luck.
Also, Online poker tournament allows its players to compete for huge money from the comfort of their homes and the spectators are also watching them via live streaming from their homes.
Watching someone battling it out against a Slot machine can become boring very quickly....
I can add that it is easier to play online tournaments. You can show your emotions and no one opponent can analyze you. It makes bluff much easier. The spectators love to see these players battling it out, because the game is more based on skill.. and not so much on luck. Also, Online poker tournament allows its players to compete for huge money from the comfort of their homes and the spectators are also watching them via live streaming from their homes.
Watching someone battling it out against a Slot machine can become boring very quickly....
And i disagree with big wins without big investment. If you invest a little money you mostly have a long way to big wins. The same as in offline poker.