It's not like the people who actually leave care at all about it and the people who need to leave get punished for it.
I just joined a Terrace of Spring group but when I got in I noticed they had already taken down 2 bosses, I want the whole deal and I don't want to abandon a group after 2 bosses, so I left. Now I'm stuck with a 30 minute debuff for it.
In short, I think it's bloody idiotic. Because in other cases it might even punish you for being in a terrible group. No matter how much you try to talk to the group or get the group together to beat an encounter, they will still fail and YOU will get punished for leaving them.
Not sure why this debuff is still in the game, it prevents nothing.