Let's be fair to big companies and publishers, they're not as averse to new settings as much as you think. In fact, I tended to notice that most generic fantasy stuff comes from small-time fries, middleware and shovelware developers or things like that.
I mean, take Activision. They probably take the safest choices out of all companies, releasing the blandest shit possible and milking them dry. Also movie tie-ins up the ass.
But then, the few RPGs that Activision published are not like that. First, they co-published Gladius with LucasArts, a tactical console RPG with the exact historical setting we're talking about in here, gladiatorial fights during the Roman empire. Then they've published these little things called Vampire: The Masquerade RPGs.
Bethesda made one of the most bland and generic games setting-wise with Oblivion, then bought the IP of Fallout (one of the more unique takes on post-apocalyptic, mixing it with retro-futurism) and brought that back to the public surface, even if they failed to make a properly good game. Years later, they hired Arkane studios (who only did fairly generic fantasy before that) and made/let them do a new game in a few and fairly unique setting.
Bioware for most of its lifetime has done fairly safe choices. First three games were D&D, then a game based on a successful franchise, and lately only pushing sequels to their generic space opera and "dark fantasy" games. The only one that feels truly out of the ordinary for them and RPGs in general is Jade Empire ... published by Microsoft.
Same with Obsidian. You'd imagine Sega would make them do a Phantasy Star or a Sonic RPG, but no. Instead, they let them do an espionage RPG, Alpha Protocol that is.
And that's just on the RPG front, in other games they often go to wild territories setting-wise with no issue. Like Rockstar, the guys who have one of the most successful franchise of games in history, they've developed/published a Wild West open world game AND a noir/detective game.