Because when things become a grind, you look for the fastest possible way to get through it. By chain pulling and just AoEing everything down, you get through the dungeon significantly faster which means you can get your daily out of the way sooner.
As for how to deal with it? You can't. You can either heal them and go or you can get kicked from the group (unless, of course, you're in a like-minded group that wants to take the scenic route).
If you want to take your time through dungeons, I would recommend manually putting a group together.