One possible reason could be a threat from Iwa to Konoha. If Iwa was planning an unprovoked attack on Konoha, Naruto might take it upon himself to destroy Iwa to protect his village.
Maybe there was some sort of evil force in Iwa that Naruto had to eliminate. For example, if there were rogue ninjas in Iwa who were causing chaos and harm not only to their own village but also to the surrounding areas, Naruto would step in and destroy the source of the problem which is Iwa in this case.
One possible reason could be a threat to Konoha. If Iwa planned an attack on Konoha, Naruto, as a defender of his village, might take the fight to them and end up destroying parts of Iwa in the process.
There might be characters from Iwa who oppose Naruto. For example, the Tsuchikage of Iwa would surely be involved as the leader of the village Naruto is attacking.
Maybe in the 'naruto neglected iwa fanfiction', there's a story where Iwa has a secret technique that could have been useful in the great ninja wars, but because they are neglected, they are not invited to share this knowledge. As a result, a young Iwa ninja goes on a journey to find a way to make the other villages recognize their worth and the importance of their techniques.
Sasuke could be involved. He and Naruto often have intertwined stories. Sasuke might either be an ally in Naruto's destruction of Iwa, or he could be there for his own reasons, like seeking power or revenge.
Naruto is obviously a very popular character in these fanfictions as he is the main character of the original series. In Iwa, characters like Deidara (who was originally from Iwa) often make appearances. His explosive jutsu and unique personality add a lot to the stories.
One great Naruto Iwa Admiral fanfiction is 'The Stone Admiral's Ascent'. It has an interesting plot where the Iwa Admiral character shows unique jutsu and strategic thinking. It really delves into the character's backstory and how they interact with the Naruto universe's existing elements.
Maybe he feels ostracized in Konoha. If for some reason the villagers still don't fully accept him despite his heroics, he could be lured by the idea of a fresh start in Iwa.
Well, he might face a lot of challenges. The people in Iwa could be initially hostile as he's from Konoha. He'd have to prove himself. Maybe he'd learn new jutsu unique to Iwa's style.
Well, Naruto might face a lot of challenges in Iwa. He could encounter new types of jutsu that are unique to Iwa ninjas. Maybe he'll make some new friends or foes there.
One interesting 'naruto and iwa fanfiction' could be about Naruto going on a mission to Iwa and befriending some of the young shinobi there. He might learn about their unique jutsu and in turn teach them some of his own skills.