Why do TV shows define Furries as people who have sex in animal costumes?
Television producers are business people who have a responsibility to their company and stockholders to make money, typically through advertising revenue based on viewership. Unusual and salacious subjects typically attract larger audiences and thus earn them more revenue. Put simply; Sex Sells. A show about Furries having sex in animal costumes, or perhaps a more mainstream science fiction fandom, such as Trekkies having sex in Star Trek uniform, will sell more advertising regardless of whether these shows are fair or accurate portrayals of these groups as a whole.