Why do people want dog breeds on tv when the dog acts horribly?

Like for example:Marmaduke and Beethoven..the great dane in Marmaduke is badly behaved but many people want one after seeing it on tv. My mom has been volunteering at the humane society ever since I was little and I volunteer there now too...I have never seen a purebred great dane at that shelter, but after Marmaduke was released there were 4 surrendered within a few weeks.One pup had to be put down because her back leg bones were overgrown and she was no longer able to walk..there other 3 were sent to a great dane rescue.The reason for surrender on all 4 was : " grew larger than expected," "ears didn't stand up"(its ears weren't cropped," "didn't get along with the cat like we thought it would" and 1 person even said "The dog did not act like Marmaduke at all,My son doesn't want him anymore" So this kind of upsets me...Why do people pick out the dog breeds that act bad on tv(even though they really aren't and it depends on training,etc) and expect the dogs to grow up perfectly and well behaved?