why so mean?

[Niwashi]

Because a lot of "noobs" don't listen to the advice given. So we've become jaded about giving wasted advice.

I don't think that's true. While rude players are a minority, rude newcomers or those who won't try to take advice are such a minuscule minority it would be unlikely you'd ever meet two of them. The problem is that a lot of experienced players say things they may intend as "advice" but which are completely meaningless to an actual newcomer. If you give someone advanced high-level instructions when they're still trying to work out the most basic aspects of controlling their character, they aren't going to suddenly be able to play as though they've been playing MMOs for years and have run this specific content a hundred times. Too many players regard that inability to accumulate years of experience in a couple seconds as meaning the newcomer "doesn't listen", and then they get mad at being "ignored" by someone who never had a chance to do anything else.

Of course, part of the difficulty lies in the fact that the person giving the advice likely has no idea what experience level the newcomer is actually at. That same advice that's complete gibberish to one new player may be just the piece that another new player needs to bring together a lot of half-understood information. The result (from the advice-giver's perspective): One player was told this and got better, another player was told this and nothing changed. So clearly the one that didn't change must be ignoring me. It's taking the only pieces of information available and forming an erroneous conclusion from them.