Why does the narrator get in touch with Simon Wheeler?

Mark Twain sets up "The Celebrated Jumping Frog of Calaveras County" as a frame story or frame narrative: a story within a story where the outside story sets the stage for the inner, or main, story.  In the case of "The Celebrated Jumping Frog," the narrator learns the inner story of Jim Smiley and his jumping frog from Simon Wheeler, described as "fat and bald-headed, and [with] an expression of winning gentleness and simplicity upon his tranquil countenance."  The narrator is visiting the mining camp of Angel's in the Western United States, and before visiting, he is told by a friend that he should seek out this Simon Wheeler and ask about the Reverend Leonidas W. Smiley.  When the narrator asks Simon Wheeler about this reverend, Wheeler instead tells the narrator the story of Jim Smiley and his jumping frog.  The narrator says about Wheeler:

he backed me into a corner and blockaded me there with his chair -- and then sat me down and reeled off the monotonous narrative which follows this paragraph. He never smiled, he never frowned, he never changed his voice from the gentle-flowing key to which he tuned the initial sentence, he never betrayed the slightest suspicion of enthusiasm -- but all through the interminable narrative there ran a vein of impressive earnestness and sincerity, which showed me plainly that, so far from his imagining that there was any thing ridiculous or funny about his story, he regarded it as a really important matter, and admired its two heroes as men of transcendent genius in finesse.

Basically, the narrator is trapped into hearing this story for its duration.  The only way he escapes is when Wheeler is distracted at the end by someone calling his name.  The narrator then knows that he has been tricked by his friend back East into listening to this story, perhaps the same story that his friend had to sit through when he originally encountered Wheeler.  This frame sets up the humor that is found in the inner story of the jumping frog and all the other curious animals that Jim Smiley bets on.