White people are overrepresented in writing and as the presumed audience.
A Trope in Agregate. The vast majority of fiction and media productions (as far as North America/the United States is concerned) is written and created by White people, for a mainly White audience. Of course this varies depending on the racial make-up of a country, but Hollywood is also a top exporter of programming. This is slowly changing as more demographics gain influence in not just the entertainment world, but in politics/social movements, but the old status quo is very hard to change. In 2013, the WGA reported only 15.6 percent of overall TV writing staff were minorites and remaining underrepresented. White writers/creators are more prolific and successful in America for several reasons. For one, White people make up the majority of the population in the U.S., so naturally in any given profession, there's going to be a lot more white people than other any other race in it. However, there is still a higher barrier for entry for those of belong to a racial minority to enter any given creative industry. This leads to the use of racial stereotypes in fiction, some more uglier than others. Since racial minorities had very limited power in the creative industries, this led some of the more racist creators putting their prejudices in their writings. These manifested into racial minorities falling into common tropes and types throughout history. Today, a good many of those old stereotypes are looked at as disdain, but still show up far too often in modern fiction. Some of this can be unintentional. As stated before, White people make up the majority of the United States, and some writers may have little or no experience dealing with other races in their lives and stereotyping is used just as something they're more familiar with. And then there's Positive Discrimination in which writers may what to dodge any sort of controversy and make the Token Minority perfect in every way, but shallow as characters. The audience at home is also assumed to be mainly white, so fiction is tailored to their perspectives and desires (or what writers think are their perspectives and desires). Tropes such as White Male Lead and Humans Are White have white characters being used prominently to appeal to the widest audience as possible, even for works that are exported beyond the U.S. Racial minority viewers are usually stuck trying to identify with the Token Minority or finding their own avenues for arts and entertainment, which of course aren't as big as White companies. This is one of the main causes for Pop Culture Isolation. See also Monochrome Casting, White Male Lead, Race Lift (in terms of "white washing"), Missing White Woman Syndrome and Minority Show Ghetto. Mighty Whitey, White Man's Burden, Humans Are White are common manifestations of this trope. Also see Most Writers Are Male, Most Gamers Are Male, and Girl-Show Ghetto for a similar construct, but mainly pertaining to gender.