I guess a big part of the problem is that races in this setting are heavily segregated, in terms of their themes. You’ve got humans with their late-medieval aesthetic, full of castles and knights and plate armor, working alongside the gnomes, who wield exotic technology that defies science as we know it.
In any ‘realistic’ setting, this would cause human society to undergo a technological revolution as they abandon their previous methods in favor of the absurdly advanced technology of the gnomes. Knights in shining armor would be no more.
However, Warcraft is a theme park setting that revolves around having all of these different themes to cater to different players. If you want to roleplay a late medieval knight, you’ve got humans. If you want to roleplay a technological wizard straight out of science fiction, you’ve got gnomes.
Once in a while, you might see a little bit of overlap in the form of skyships and similar things, but that’s as far as it goes. These vastly different races just don’t learn from one another or affect one another, for the purpose of maintaining their distinct identities in the theme park.
The only outlier of this is the Iron Horde but even then, that got confined to its own specific corner of the theme park as well. Only the Mag’har use iron stars and Iron Horde technology because that’s their theme, and the rest of the Horde doesn’t even touch the stuff.
Now, I’m not going to say that the ‘GoT roleplayers’ are right. They shouldn’t completely isolate themselves and ignore the rest of the setting. However, there is nothing wrong with creating a character or even a guild that’s focused on the medieval knights of the humans and focusing your roleplay on that particular theme of the setting.
You shouldn’t pretend that advanced magic or technology doesn’t exist in the setting, but I wouldn’t blame anyone for distancing themselves from it if it’s not a theme they want to play with. Sometimes you just want to focus on one of the many themes that Warcraft caters to and yes, one of those themes is the low-tech medieval knightly kingdom of the humans, which does cater to fans of Game of Thrones.
They shouldn’t police your roleplay just because it doesn’t match their theme, but you should try to respect the theme of whoever you’re roleplaying with too.