maybe they actually just thought "Hey, we want us some CoD!" and robbed it without thinking out how poorly protected it is.
edit:
it makes a better story thinking it your way, so i'll think that instead.
that's handicapped. its extremely obvious this was done by criminals in it for the monetary gain.
no one that just wants to play it a few days earlier is sophisticated or dedicated enough to plan something like this. its not like the truck's route was announced to the public a month in advance.
you don't steal 400,00 euros worth of ANYTHING on a whim or without planning it for a long time.