True - lengthy prison terms would serve to deter others from doing it, but there's always someone who thinks they're smarter than management.
A reason why they SHOULDN'T be put in prison for too long is to recoup losses. It's liek folks who make mistakes ( either intentional or by accident ) on thier taxes. If you put them in jail, then you're taking them away from any potential to pay what they should. ( we're talking about anyone under 'wealthy' status)
So putting thes embezzlers in jail for too long would mean we don't get the money back at any significant pace.
Maybe some Community service where they HAVE to divulge what they did and who to regularly, might be a mor effective punishment. I've always thought that Social Ridicule is one of the most powerful behavioral Modifiers out there ( although it can make a twisted person even more twisted)