Story time with Ewitt Rainbow
A long time ago in the times of ARR,
People would pull all mobs to the dungeon boss.
Even if a player was new it became the meta. Which for many causal player was very overwhelming.
Some dugeons that would normally take 18-20 mins were getting completed in 10-12
See: https://www.youtube.com/watch?v=12DdeN568gc
This for many people wasn't fun indeed it was stressfull, and if you did whip people got upset and it could take longer then if you just did things normally.
Also if you didn't pull fast enough people would just leave the party. causing everyone else to have to wait.
I did a few speed runs in my day it was ok for me. But my hubby HATED IT, and it turned gaming into work.
But every party was trying to go as fast as posiable.

So they walled off content to slow down people and make every dugeon a 15-20 min task.