The story suggests that the majority of the audience came of their own accord for the sheer entertainment aspect of the semi-barbaric king's arrangement. The narrator praises the the king's arena, noting:
"The institution was a very popular one. When the people gathered together on one of the great trial days, they never knew whether they were to witness a bloody slaughter or a hilarious wedding. This element of uncertainty lent an interest to the occasion which it could not otherwise have attained."
The uncertainty of these execution-wedding events kept the masses "entertained and pleased," and Stockton includes the detail that even the thinking members of the community supported the practice of the arena, because the choice rested solely in the hands of the accused. One can imagine that the events of these arena-style trials were the fodder for gossip and discussion for many days or weeks among the common masses in the kingdom.
No, the audience members went to the arena because of the environment they lived in and fear. The King is described as being semi-barbaric in the story, the concept of barbarianism promoted fear in the hearts of the people living within the village. This reminder of capital punishment was a deterrent to crime. People went because they were scared and it reminded them to not break any of the King's laws.