In The Notorious Jumping Frog of Calaveras County by Mark Twain why is Simon Wheeler so eager to suggest to the stranger that they bet on his frog?

"I found Simon Wheeler dozing comfortably by the bar-room stove of the old, dilapidated tavern in the ancient mining camp of Angel's, and I noticed that he was fat and bald-headed, and had an expression of winning gentleness and simplicity upon his tranquil countenance. "

Twain characterizes Wheeler as a fat, bald-headed man that had an expression of winning gentleness and simplicity.