I'd never taken an accounting course, never run a business, never even had savings of my own to manage. I'd stumbled into a job at Salomon Brothers in 1985, and stumbled out, richer, in 1988, and event though I wrote a book about the experience, the whole thing still strikes me as totally preposterous—which is one reason the money was so easy to walk away from.—The Big Short by Michael Lewis—
Hello, I wondered the meaning of part "walk away from" while reading this phrase. I assume money walking away from him after he got richer but I wonder what reason made money walk away here, is it his lack of his money managing skill or thing that was preposterous?
Also I searched a meaning "walk away" in a Lexico Dictionary and I don't get how casually or irresponsibly if money would withdraw.
Casually or irresponsibly withdraw from a situation in which one is involved or for which one is responsible.(Lexico Dictionary)