I recall Finland had a rule that you can listen (how else would you hear the next message meant for you on maritime VHF), but you can't repeat things publicly or act on knowledge gained from that. Now, why would that be? Well, it's mostly to minimize sensationalist news reporting of people's accidents, misfortunes and such, whether maritime or over old school police radio (before it was encrypted). Discourage ambulance chasing, that sort of thing. It's just another part of the European attitude toward privacy.
I think a number of countries have this sort of thing. It's more, as you say, not banning the listening but if it can be shown you acted on it then that's the no-no. This was probably more relevant in the times of unencrypted analogue cordless telephones and cellphones. The sensationalist news thing is a good thought too.
