Why is the spoken German in many US films and TV shows so inaccurate?

It would be interesting to see if the inaccuracy of languages in US productions correlates with the number of speakers of them in the US. As suggested on the linked page, one explanation for the poor German is lack of sufficient German speakers to check it. This could be compared to see if the spoken Spanish is better and if more obscure languages are worse.

Probably because it's there as "greek". Something people aren't supposed to understand --just a prop.

My favorite is one of the scenes in "Lost in Translation" where complex sets of instructions are distilled into a single sentence.