Toxic Environment.

[Februs]

Easy to be nice in a non-competitive environment, when you get what you want.

Exactly this. Competitive environments actively bring out this kind of behavior. It's not even exclusive to an internet environment. Ever been to a live sporting event? Worse yet, ever participated in one? There's no end to the salt and pepper when it comes to competitions. It's been like this since the dawn of time. In comparison to other online games, the comment box in FFXIV is downright polite.