Why did Cardinal block Yui from relating with players?

Question

I just finished watching SAO, and I'm not sure if this is ever explained:

Yui is a program that supports the psychological health of the players. She states that, for some reason, Cardinal did not permit her to relate with the players, and was limited to observing them.

Why did Cardinal block Yui? Is this explained in the novel perhaps?

If Kayaba created SAO, I'd guess that he also made Cardinal and Yui. I doubt that he'd want to block his own creation from doing its job, so I guess that the fault is entirely Cardinal's.

Answer 1

I just searched for the part in the novels - It's the third part of the second novel. But I'm sorry to disappoint you, there's not much explained:

(Source: Baka-Tsuki)

"Although I am unaware of the complete details of what exactly happened as well, Cardinal handed down an unplanned order to me. A complete prohibition from interfering with all players[...]"

Asuna reacted reflexively; she guessed that "unplanned order" was due to the manipulation done by the only GM of SAO, Kayaba Akihiko.

I guess it was developed by many people who planned to add this feature but Kayaba just decided to disable her without letting the other developers know.

Answer 2

I don't think Kayaba worked on SAO alone. This is never explicitly stated. It's likely he had a large part in it, and created most of the core, and designed most of the elements of the game, but I can't see one guy creating everything alone.

Yui was possibly created by someone else who worked on the game (Or possibly even Cardinal). SAO was the first real VR Game, so the effects of being inside a VR world for long periods of time weren't really known. The Cardinal System was created with the intention of being self-managing, so that humans were never needed, to manage to game, or even to update/patch the game. A program to take care of a player's mental health (to possibly avoid law-suits?) was probably part of the plan for that.

Here's a link to a translation of a sort of "Q&A" that the author had with fans, and characters of the story, back in 2005 (when SAO was still a web-novel.)

Q. Did you know about Yui’s existence?
A. I didn’t spare it any attention at all, a great opportunity gone by.

From that, you can infer that Kayaba himself didn't create Yui.

Answer 3

She was there to support players and keep their psych in top condition. The moment the game kept people inside, Kayaba most likely forced her to stop for his "sick game of death".

After regaining her memories, she tells her in-game parents that she had become melancholic when the death game began, as she wasn't allowed to comfort players and was forced to continue monitoring their psychological parameters, but, after nearly 2 years of only seeing insanity, misery and anger, she finally noticed a couple that showed happiness and joy and wanted to be close to the two to experience their emotions, even though she was not allowed to interact with players.

Answer 4

Another option, are, even if all system are programmed by one or multiple persons, Yui are here as a part of Cardinal System, and The Seed. All the system are programmed not only for SAO, it's ready for creating more worlds (end of ALO words of Kayaba).

It's the same as the link between The Seed created games. These system are present on SAO too (probably), but, you cannot view it because there isn't more games, or, these system are explicit disabled.

Another option are, Cardinal disabled Yui itself, because Yui have GM privileges and can logout players if they're in too bad mod (something stupid in a game without logout button).