He deposited-in today's dollars-$53,363, so it wasn't money. He was no kid; 16 years is a long time to be away. No love lost with the brother.
Did they mention it and I missed it?
"It's the system, Lara. People will be different after the Revolution."
I think someone said that when he was drunk in Chicago, the guys(other soldiers?) who put him on the bus heard him say he was from Parkman, so they put him on that bus and told the driver to take him there.
Perhaps he was looking to head somewhere else with his money, or to stay in Chicago. The story is set in 1948, sometime after the War.
I like how Sinatra awakened on the bus to discover that his "Chicago soldier friends" had put his wallet down the front of his pants, in the crotch, to avoid him getting robbed. Sinatra grins knowingly and in thanks to those unseen guys. A nice "saucy" touch in a 1958 film.