It's common throughout human history. If gladiatorial contests were broadcast on TV today, is there any doubt they would be wildly popular?
It's not like football is that much better. The Gladiators didn't go out and fight with the intention of killing each other, but it was vicious, violent, and bloody and sometimes they DID die. They couldn't have them fighting to the death regularly, they took too long to train, they'd have run out of Gladiators.
(that doesn't say anything about the criminals and political prisoners and animals that were butchered in the Arena. THAT is where the REAL blood came in)
We have professional wrestling, "reality" shows, Fear Factor ... gladiatorial contests with everything but the coup de grace.