"Speaking Mandarin Chinese" in Hollywood

It's quite often to see some scenes in either TV shows or movies that the characters speak something they claim to be "Mandarin Chinese". Some characters even claim to be very fluent in it. However, for a native Traditional Chinese speaker from Taiwan like me, most of the time, those so called Chinese on screen can hardly be understandable, if it could be understood at all.

It is quite strange, since there should be lots of native Chinese speakers near the production locations of these shows or movie. Is it that hard to find a decent language consultant to make sure the proper pronunciation of a few lines? Or the Hollywood just too proud to admit the fact that, they can't do it right when they are so self-centered and so used to laugh at those whom didn't speak proper English? It's quite painful to hear a character you love to speak something that has nothing resemble to what they claim to be, if that "thing" could be called a language at all.