Because many players new to a dungeon expect others to type out what is already written out in a guide on certain websites. So instead of someone looking on the internet, they eexpect others to type out the exact same thing in party chat when they enter.

How many times do you see, "I'm new, what do I do?" or variations of. Or not even saying anything, even when it pops up theres a new player and then proceed to ask who's new to be met with silence?

So whats the difference between reading up beforehand and expecting someone to teach you after? One is using initiative, the other is putting demands on others who shouldn't be expected to cater to you, that's being pretty selfish and self centred. Players taking time to explain and give advice are a bonus, not your right to expect!