Skilled played find tanking boring because when they tank everything goes perfectly. Mobs are always under control, damage is mitigated well to make healing easy, and it turns everything in a mundane snoozefest.

Bad players find tanking difficult and frustrating because when they tank everything goes to hell. Mobs run around and assassinate people, they don't manage their cooldowns well so they take huge spikes of damage making the healers work overtime.

That's why both skilled and bad players tend to stay away from tanking.

If DPS is bad nobody really notices, it just makes boss fights take longer and make healers work a bit harder but runs are still smooth even if DPS is bad(all 8 man content can be done with 7 people in this game)

If Healers are bad usually you don't notice. Healing is extremely easy in this game(good healers spend 80% of the time in 4 person dungeons DPSing, only needing to heal 20% of the time) and all 8 person endgame content can be done with 1 healer, yet most groups do it with 2 healers so 1 healer can be carried.

Bad tanks are instantly noticed because having 1 bad tank makes everything go to hell.