Why wasn't Aang trying harder to reconnect with the Avatar State in Book 3?

Question

Given how long it takes to master elements, Team Avatar should have realized they probably couldn't make much of a difference in Book 3 just by training bending abilities during the short amount of time they had left. Why didn't they try anything to reconnect Aang with the Avatar State? As it was proven repeatedly, it's the best advantage they had against the Fire Nation.

Aang was basically fixed by getting hit in the back with a pointed rock. They could have tried to find the guru again, and maybe he would have given a massage or something that would have brought back the Avatar State. In the discussions preceding Sozin's Comet, the characters hardly mention this superpower, the only real chance Aang had against the Fire Lord.

Why didn't Aang and friends make any effort to bring back the Avatar State? The way the writers did it really seems like a deus ex machina. It meant that Aang's victory hinged on the small chance that he gets slammed into a rock in the right way. Not only was the guru alive, but Aang also had the wisdom of all past lives, some of whom might have had the knowledge to help.

Answer 1

The guru seemed pretty definitive when he said Aang turning away from the Avatar State when he did would render him locked out forever. And no doubt Aang remembered the whole rigamarole from the beginning of season 2 when he tried (and failed) to deliberately enter the Avatar State. So he no doubt thought trying would be a waste of his time.

Remember too that their plan, both before and after the Day of Black Sun, was for a decapitation strike against a few specific high-ranking individuals; Aang probably thought he could handle them with his ordinary bending - particularly since he has the advantage of using (at that point) three different disciplines against his opponents' one. As it turns out, he was catastrophically wrong in that assumption, but he didn't know that at the time.

Answer 2

The show stated multiple times that if the avatar dies while using the avatar state, the avatar cycle ends. That means no more avatar forever¹.

The last time he had used the avatar state before book 3 was in a fight against Azula and a number of fire nation soldiers. That did not end well. If he tried to pull the same stunt in the heart of the enemy's forces, he would surely die and there would never be any hope of a new avatar arising to bring balance to the world anymore.

Aang using the avatar state against the Phoenix King might have been more of a calculated risk from his past lives. He was facing just one enemy there, not a whole army.

¹ Taking what we learn in The Legend of Korra into account, the cycle might be restarted, but it would take decades in the very least, or multiple cycles of light an darkness (at 10,000 years each) in a worst case scenario.