Especially at banks. Very embarrassing and not worth the attention it would garner if they pressed charges. There are a lot of financial institution that have very weak controls. I've seen it first hand.
One bank had guys in the IT department work for a couple of months then quit, one after the other, apparetly after having stolen 'enough' money (whatever that means to a thief). Rinse and repeat, till their company got called in. That bank's systems were apparently that bad.
I always wondered whether it was that the bank had no proof of the theft or an image thing where they could not afford to go after them because customers would lose confidence in them.