Granted, it's the Internet, but I remain dismayed at the common sentiment in fantasy gaming circles that somehow associate single-race fantasy campaigns with "boredom". However, I didn't encounter this first online. I encountered it in-person, over 20 years ago, when I wanted to run the sort of Dungeons & Dragons games I first played in the early 1980s when I played the Basic version of the game.
It's still seen now, and you don't have to look hard to find it in tabletop RPG circles, but you don't find it in videogames much outside of a few that try to hew as close to D&D as they can without crossing legal lines or hitting technical limitations.
In short, what it comes down is the misconception that "culture" equals "race", and therefore All (X) Are Like That. The reason this persists is because it's fucking easy shorthand under the standard gameplay paradigm of multiple playable races being allowed for players' characters, but if you cut it down to two or one then you can't fall back on being (X) and instead have to properly individuate your character- and often without any mechanical structure to rest that upon.
That this remains a persistent enough element of gamer psychology, such that games are praised or wrecked by how well it facilitates it, tells me that most tabletop RPG players really don't want to do that sort of thing in their gaming. (And yes, this is old; it's one of the biggest knocks on things like Empire of the Petal Throne, and contributes to the ongoing depreciation of historical tabletop RPGs vs. their fantasy counterparts.) They want easy icons or archetypes--the sort in bad movies--and not to do fucking acting; think classic Hong Kong or Hollywood action films. This is why bad movies make for good gaming.
It's part of a thing I've noticed over the decades that I sum up thusly: "People will not work for their entertainment." Very few people enjoy doing the work that proper characterization requires; for most, being a static archetype at all times is preferable because they can just get on with what they're there for: playing the fucking game. Entertainment is meant to be fun, and therefore easy and enjoyable; making a player do otherwise is to ask them to do work- and gaming isn't about doing work.
Want to know what sci-fi RPGs are popular? The ones with lots of playable races. Fantasy? Lots of playable races. This is why Shadowrun was always more popular than other cyberpunk RPGs, and why RIFTS is Palladium's top-dog RPG for over 25 years (even over their fantasy RPG). They won't put in bitchwork for fun, so they use easy symbolism as shorthand; take away the symbols, and they find their fun diminished, thus they're bored and find it boring to do that.
It's a bothersome quirk, but I can work around it- even use it to my advantage. Most can't, or won't, so the issue persists and its adverse effects upon all forms of RPGs (but most felt in tabletop RPGs) also persists. Until this attitude changes, there's no fixing it.