Is "forfeit what you've got and go to jail for 18 months" harsher than that? I'd pick the one that let me get a clean start after.
And in the case that it wasn't spent, and by fine you mean as a replacement for any forfeiture, not in addition, then sibling comment has a great point that "if you get caught, you just gotta give it back" is an incentive to commit fraud, not one against committing fraud.
Prison for theft is so brutally cruel. Who was really harmed by this once he paid the money back? A line item in some megacorp that was lower for awhile?
No one felt anxiety or pain, the megacorp probably barely noticed. Pay them back with interest, move on.
Obviously the calculus changes for violent thefts, or breaking into someone's home. Those cause real emotional impacts to people. Of course simply returning those items doesn't make someone whole.