I actually dont think this is true. Ive seen advise given quite often. Its just not often taken in reality. You have to consider this from a basic standpoint: If youre in a group with someone, it is assumed broadly that you both share the same goal. You know, complete some content. If you witness someone in your group not performing well, you can do 1 of two things broadly: Not say anything, or try say something in an attempt to address an issue you see. Pragmatically so you have the best chance at success, its better to offer up something that actually corrects the issue. While there are people who do use the "God you suck, Git Gud scrub" mentality, most players dont go this route out the door. Simply because saying that is almost guaranteed to piss the other person off, you arent addressing any real issue that they can work with, and its more likely to ultimately shaft your group dynamics resulting in you failing to get something done. So its better to say some piece of advice.
The trouble I see more frequently is how that advice is taken. People dont like to consider themselves bad at things, or that theyre doing things wrong. They usually like to think "Hey, Im good at this. Screw this guy." Its a bias people typically have for themselves. Human nature and all. So advice is often seen as criticism, from my experiences. Which sours people, and then things go sideways.
To be frank, you had a bad WoW group. I do know there are players who are of the mindset of "Learn it yourself, youll be better for it." But I dont share that opinion. Being encouraged to ask questions, especially from people who know the subject matter, is more expedient than being told "Git Gud," and "Go look it up." It really comes across as stupid because if a person has knowledge on how you can improve, but is refusing to share it, their advice then becomes nothing more than criticism and sneering. And to be clear, I dont mean people who give you an overview of what youre doing wrong and then rpovide you with direction to delve deeper. Im specifically talking about people who say "You need to get better. Do X." but then when you ask them about it in depth, they tell you to go read a guide. If they know the material but arent willing to help you when you show interest in being better, thats more on them.