That trope can definitely be frustrating, especially when it’s done without research or care. Though sometimes in collaborative RPs, to play devil’s advocate a little, is that the distribution of cultures ends up uneven simply because people are going to gravitate toward what they personally enjoy writing, not because the GM wants a token desert culture or anything like that. 

Plus, most people here are writing as a side hobby. Not everyone feels confident portraying cultures outside their own in detail, and forcing it can lead to worse outcomes, like shallow caricatures or stereotypes. Personally, I’d rather players write what they understand and enjoy than feel pressured into hitting some kind of diversity quota for a small RP group.

And honestly, in a lot of cases, I think it’s more important for the focus to be on how characters are written, not what race they are. A ton of work can go into personality, politics, relationships, lore, flaws, motivations, i.e. the things that make characters feel real. The faceclaim or cultural aesthetic is just one piece of that, not the substance, I would argue.

At the end of the day, this is supposed to be fun. A few writers choosing similar aesthetics doesn’t automatically mean the worldbuilding lacks depth. All it usually just means is that a handful of people happened to share tastes at the same time.