Look at this way: A bank is fined $x for doing an action which generated $y. If x < y, there is no incentive to stop any behavior. Further, it seems to be the trend that y is far larger than x and this case proves it out.
The libor scandal cost the U.S. at least $6 billion in interest charges (y) and another $4 billion just to unwind their positions. Whereas the banks have only been fined $2.1 billion to date (x). When you take inflation into account and the fact that this is a world wide financial scandal (libor influences a $350 trillion derivatives market), the math is skewed even heavier in the direction of banks having had a sizable revenue stream after the fines.