Implausible setup (spoiler)

I can totally see why a gangster would like to have someone store his illicit money for him while he is in jail. But why on earth would he turn to a degen gambler? That’s literally the last person in the world you should ask to do that job.

Because sure, like anyone with half a brain they are going to be afraid of incurring your wrath if they outright steal the money. But unlike anyone else, they will convince themselves that it’s not a problem because they are only borrowing the money and will make back well more than enough to cover what they take out. So they are actually much more likely in the end to take the money than someone who is contemplating just stealing it but will probably reconsider because of the danger. The gambling addict doesn’t see the danger!