Gambling for that long is a way to launder money. You play for a long time losing a very small amount of money. At the end of the night you get a fresh set of bills in cash. Or you get it in an account and you can take it out of the ATM. Or someone else can. There is no path from accountant to real estate flipper to multi-millionaire to excessive gambler. He must have been a cheat somewhere along the way.
I think with a father who was a bank robber, the accountant figured out a scheme. He needed to launder the money and explain his wealth, so he gambled in the game that had the lowest lose percentage. So he lost 3%. But he laundered 97%.
I have a few guesses as to what was going on:
His father had a lot of money somewhere and he was laundering it before he used it.
He figured out how to rob a company that he worked for. and used the gambling to hide the income.
He was part of the mob or other criminal group. He would pay people out through his gambling accounts.
He was being paid to buy and sell guns. He would get cash. Gamble it and take it on account. Then he could write a check off his casino account.
He flew money into the country, (or out) and he needed to get it in the credit system.
An extremely private accountant, who gambled constantly for 20 years, with a pilots license and a gun license. This guy has too man ways to cheat the system.
He was playing poker in the casinos, and was good at it.
My older brother made money playing poker. It was his hobby.