Hell even if not on purpose. The point of a board is oversight. If management can commit illegal acts without the board's knowledge, the board has failed. Of course incompetence in a board role shouldn't lead to prison. But it should at least bar someone from future board jobs for a few years.
Pour encourager les autres. If there's illegality going on at a company and the board doesn't know about it, future boards will make sure they are better informed.
It is extremely rare to see that kind of prosecution in western countries (US or EU).