Some blame a dearth of source materials. Even in the day of Holmes the Physician - examples of fantasy and SF fiction where protagonists and characters aren't white existed. For example the Earthsea series by Ursula K. Le Guin. Which makes the TV version of Earthsea by Sci-Fi with it's white protagonist jarring. And when Le Guin says this thirty-six years later, you have to ask what's up with the status quo.
"I have received letters that broke my heart, from adolescents of color in this country and in England, telling me that when they realized that Ged and the other Archipelagans in the Earthsea books are not white people, they felt included in the world of literary and movie fantasy for the first time."The quote is from Pam Noles' essay Shame, a poignant study of why representation matters. Yet arguments persist that tabletop RPGs are a Caucasian thing, a view ignoring the existence of Japanese RPGs, industry figures like Louis J. Porter and fans. These arguments support a primary demographic of... Comic Book Guy. Fortunately there is more in heaven and earth than dreamed of in that philosophy!
-- speech to BookExpo America children's literature breakfast (2004).
It's been argued versimilitude is a problem as characters of colour can't use the equipment of their Western peers and may need historically accurate costumes leading to racism and stereotyping. For a moment, let's indulge the quixotism in championing historical fidelity for games with dragons, wands of fireballs and Cthulhu. Why wouldn't a warrior with access to plate mail use it? Plate mail was found from Spain to Japan.
Even with concerns over other cultures using European arms and armour, positive examples exist. The 12th century Moorish warriors of al-Andalus used Frankish crossbows and wore mail like Christian neighbours while using better-quality cuirasses in place of heavy breastplate. Fears of appearing racist seem unfounded when it comes to this issue.
Rather, be concerned when white separatists calling for a boycott of the Thor movie over Idris Elba playing Heimdall claim support from irate comic book guys. Presumably Tadanobu Asano as Hogun The Grim and Natalie Portman as Jane Foster isn't a problem? Never mind Marvel's Asgard differing from the home of the Aesir. Or the Viking propensity for assimilating into foreign cultures (e.g. Normans, Rus, Varangians)...
Greyhawk, Golarion and the Forgotten Realms acknowledge the appeal of world cultures with places like Ket, the Minkai Empire and Rashemen. The presence of games like Legend of the Five Rings and Nyambe prove settings outside medieval pseudo-Europe are commercially viable. So is the question merely one of accessibility? Of opening the eyes of the audience to an unfamiliar world?
Writing a different culture is not without risks. There is a fear of appropriation in portraying a different culture. Of using masks rather than getting under the skin. Adequate research, hard work and a dash of empathy are needed. Such endeavours need work and risk crashing and burning. However, this is the strength of tabletop RPGs, the ability to try and imagine another person's life while having fun doing so. What better challenge?