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....
This is what makes poker so exciting to watch, watching someone playing against a machine or a computer is nowhere near as exciting as watching that person playing against another one, I do not know exactly why this is the case but it makes it way more interesting and it gives poker an edge over other gambling games, maybe slots are way more popular than poker but poker is way more interesting to watch as the plays some of the world experts can make are incredibly impressive when we take into account the money they are betting and the level of their opponents. 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....
Base skills games usually have tournaments not unlike those based on luck games.