People leaving dungeons after not getting their loot.

With the release of TWW, I noticed that more and more people just leave the dungeon group after killing the boss they are trying to loot.

It is getting extremely annyoing as it happens in almost -if not all - dungeons.

Has this always been the case the first weeks of an expansion release or is this normal?

It's so annoying and I was wondering if others felt the same way.