Why has Korra never turned to Raava for advice or guidance?

Question

Book 3: Change is all about Korra having to deal with issues and conflicts without the help from her past lives. She feels alone, and that there is no one that truly understands her. This is shown, especially in The Ultimatum and A Breath of Fresh Air, where Korra is seen trying to contact Aang for help.

But wait!? She's not alone. She has Raava. Sure, Raava is no past Avatar, but she's been with all of Korra's past lives and arguably knows them better than anyone else. Why is Raava so under-utilised when she's a fundamental aspect of The Avatar?

Answer 1

Korra did turn to Raava for guidance on one occasion

During Episode 10 "Beyond the Wilds" of the final season of The Legend Of Korra (Book 4: Balance), Korra enters the spirit world to free Jinora and a handful of others from the spirit vines, which had imprisoned their spirits within plant-like bubble pods in the spirit world.

Just after confronting chained-up Zaheer, and after she agrees to let him help her enter the spirit world and essentially work through her trauma, she ends up in the spirit world and you can see the pattern of Raava glow on Korra's body:

Raava lights up inside Korra, surprising her; telling Raava she missed her, Korra asks where she was, and Raava replies that she was always within her. Korra asks Raava if she can help her find Jinora, and Raava transports her across the Spirit World to the missing tourists; their spirits are held captive within a large, green bubble. With Raava's help, Korra frees them; as she does, their bodies are released from their cocoons in the physical world.

-- Summary of the scene I'm describing taken from the Beyond The Wilds page of Avatar wiki

Here is the conversation between Korra and Raava (from the episode transcript):

... Raava lights up inside of Korra.

Korra: Raava, I missed you. Where have you been?

Raava: I have always been inside of you.

Korra: Can you help me find Jinora? [The wind blows Korra to the location of Jinora and Ryu's tour group. They are all trapped inside of a green, spherical force field.] How do I release their spirits?

Raava: You must bend the energy within.

Korra: But I'm powerless in the Spirit World.

Raava: No. You're most powerful here. In the Spirit World, you're connected to all the spiritual energy.

Korra walks over to the force field and puts her hand on it. Her eyes glow and the force field becomes a golden yellow, signifying the release of the spirits.

Cut to Jinora and the tour group being released from their vines.

This, as far as I'm aware, is the only time an Avatar (besides Wan) has directly sought guidance from Raava (and even then, it was more like Raava offered guidance, since Korra only thought to talk to Raava because Raava made her presence known to Korra).

Answer 2

Because Raava is not there. No Avatar after Wan has ever communicated with Raava. Her consciousness was apparently lost after the merger between her and Wan, who became the first Avatar capable of bending four elements simultaneously and entering the Avatar State.

• The Avatars, if they were able to achieve sufficient enlightenment or use of the Avatar State could commune with previous Avatars but Raava's existence is now just sustaining the Avatar spirits, it does not appear to be conscious in and of itself. No explanation for this has been given. Perhaps she was able to make the bond between them permanent but non-lethal during the special time of the Harmonic Convergence.

• As they drew near to the portal on the day of the Harmonic Convergence, Raava apologized for her prejudiced view of Wan, as she had been unaware that humans had the capability of displaying nobility and courage. In response, he reassured her that they would be able to defeat Vaatu by working together. Wan and Raava traveled through the portal to the Spirit World, while Vaatu emerged from the Northern portal.

• The dark spirit challenged Raava, but Wan stepped forward to defend her. Using his firebending, Wan attacked Vaatu, though the spirit easily evaded his blasts and retaliated with his tendrils and energy beams. Realizing he was no match for Vaatu, he called upon Raava to help him by merging their energies. Although the merge put him in mortal danger, Wan refused to give up and kept fighting Vaatu. However, the spirit managed to knock him down and pin him to the ground near the Southern spirit portal.

• When the Harmonic Convergence began, Wan placed his hand on the spirit portal, permanently bonding his spirit with Raava's. This bond created the Avatar Spirit, making Wan the first Avatar.

--Hedrick, Tim (writer) & Graham, Ian (director). (October 18, 2013). "Beginnings, Part 2". The Legend of Korra. Season 2 (Book 2: Spirits). Episode 8 (Episode 20 overall). Nickelodeon.