Yeah, I saw it on the EE Documentary.

What I found fascinating was that each 'race' was given training on how to act, move and stand like their species. For instance the Goblin Town Goblins had to have this sort of skittering, panic driven movement - like an animal always living in the moment, never knowing where it's next meal or threat will come from - which alows an audience to immediately read things into their species and lifestyle. But the moment the actors put on bulky prosthetics and masks that effectively blinded them, all of that performance was lost, and it became "dude in a suit".

Same reason the big (awesome) Bolg was scrapped for Azog (and maybe why it never really appeared at all) - prosthetics LOOK loads better than CGI, but the more prosthetics you put onto an actor, the less of their performance comes through. In LotR, the CG was orders of magnitude worse, so they had really no choice but to go full prosthetics wherever possible. The orcs looked great, but none of them were really going to be capable of pulling off a main villain role across all three movies. The actor simply wouldn't be capable of doing a performance in these instances Digital Makeup (as Weta ended up calling up) is vastly preferable, especially now that he technology is capable of, given the right amount of time, doing a fairly decent job of it.

It's why they CG the faces of most of the orcs, even the ones in prosthetics. They can get better performance out of them, and also it allows them to deviate from the standard human face proportions, which Jackson was keen to do for stylistic reasons, and to make the orcs more 'monstrous'.

Regardless of anyone's opinion on the movie, if you're at all interested in filmmaking process or understanding why AUJ turned out the way it then i can't recommend the EE enough. The appendices are really the star of the show, and worth the purchase price in themselves. The commentary is also worthwhile. Lots to learn!