There are various factors that may contribute to the terrible attitudes from my perspective and experience on Primal server:
1) I remember in the start of 2.0, I encountered more than a handful of douche-bags compared to playing around 2.2-2.5ish. Perhaps the "this game blows, I'm outta here and gracing another game with my godly presence" attitude had them leave as fast as they came, and have returned with the release of 3.0. They may skitter back to the darkness again when 3.1 or 3.2 comes around.
2) As others have mentioned, the veil of anonymity makes the bad players have an excuse to lay out anything they say with no consequence.
3) With the game being more complex, players are simmering up new play styles, and in turn find good ways of playing. They then attempt to turn their style to the "primary way that everyone MUST play," when there are many play styles to result in a clear instance successfully.
4) Relates to #3 where players force their standards upon others and with their loud-mouths, spread their standards even further to make their play style the norm.
5) People are different and some people are just plain rude, because some people talk rudely normally in their everyday life. A sociable game like FFXIV, in a way, can provide a playground for personality development.
6) Players are finding more and more ways to segregate themselves from one another in a game that requires cooperation from all parties, regardless of play style. E.G. casual/hardcore, cutscene/inn, homeowner/homeless, grinding/pacing, tank;heal/dpsing, newcomers/veterans, workers/freeloaders, etc.
7) As addressed by others, the game with it's usual lockouts, have players play the game as if it was a job, with the mentality of missing a day or week means more work to catch up to everyone else with more time on their hands.
8) See what happens when you assume. You make an Ass. of U. and Me.
9) The lines between newbie and troll are getting thinner and thinner. In my view more veterans are more inclined to assume a player that is performing poorly is a troll.