Why did i make this bet? what’s the good? the lawyer loses fifteen years of his life and i throw away two millions. will it convince people that capital punishment is worse or better than imprisonment for life? no, no! all stuff and rubbish. on my part, it was the caprice of a well-fed man; on the lawyer’s pure greed of gold.” according to the excerpt, what motivated the banker to wager the bet?

I would have to say that what he did was not a really good Idea, I mean Losing 15 years of his life is bad and throwing away TWO MILLIONS. But that's not what I would do you have to get punished for something in life or you will never learn. It will probably convince people that everything in this world has gone wrong and that people have bad ideas.  I think this motivated the backed to wager the bet because he was getting more money into his work and there is NO way for anyone to take it from him 

Hope this helps