The problem is the community has cultivated the idea that you don't have to heed any advice, either given politely or rudely since your money is paying your sub. It's those people who no matter how nicely you word your advice, you continue to see tanks pop mit at like 20% health, not use mit on big pulls, people holding CDS to use on bosses instead of trash, or players doing single target rotations when there are 10+ mobs around them. Sure people are at different skill gaps. The difference is unless somebody points out to you that something is wrong, you literally have no idea in this game due to not having any comparable feedback. The only way you learn it is by somebody telling you "hey you should do X instead of Y because of Z reason" or them watching a video outside of the game.
Except...

A.) I do see this happen. Even when going between packs or getting ready for a boss fight, there's plenty of time to put useful advice in chat.

B.) In the end, it depends on what people are interested in doing. If someone has no desire or intention to ever go into Savage or Ultimate content, they don't need to be at the skill level that content requires. As long as what they're doing is sufficient for accomplishing what they want to do, everything is fine.