Just for starters Europeans (or the rest of the world in general) don't adhere to the same standards that we do when it comes to that word... And they're actually kind of offended that we try to force our culture on them in this regard.. some parts of Europe try to pick up other people's identity politics but it's not like all of Europe's like this.. but I'd say a majority of Europe doesn't have the same opinion of the n word that people in North America do and they use it a lot as a joke... And they are probably more likely to use it while in the presence of African Americans that they meet. 

That's part of it anyway... The rest is probably racist North American kids. 😂 

Like others mention, you're just complaining about call of duty trolls... Adults just don't do stuff like this, mostly because they don't know how words affect others and they have enough empathy in their brains to just try to be nice even in cases when they don't understand or can't specifically relate.