One possible reason could be that they are too involved in their own shinobi duties. The world of ninjas is full of dangerous missions, and they might be constantly away on important tasks, leaving Naruto feeling neglected.
In this fanfiction, the reception could be mixed. On one hand, the older generation who remembered Minato and Kushina would be very glad to see them return. They were important figures in Konoha's history. But on the other hand, some of the younger shinobi who didn't know them might be a bit cautious at first. Still, once they learn about their heroic deeds, they would likely warm up to them.
The city of Gotham would also be affected. Batman has been a symbol of fear for criminals. Without his dark past driving him, there could be a power vacuum in the fight against crime. This might lead to an increase in criminal activity until new heroes or law enforcement methods emerge. Also, Batman's relationship with his villains would change. Some villains like the Joker might not have the same 'fun' without the brooding Batman they know.
His father could be Ash from Pokemon. Ash has had so many adventures and it would be interesting if he somehow ended up in the Naruto world and had a child with a Naruto - world character. His mother could be a random ninja who had a connection with Ash.
If Naruto's parents were revived in fanfiction, the plot could change in many ways. For one, Naruto's character development might take a different turn. He could become more confident with his parents by his side. The power balance in the ninja world might also be affected. Enemies might think twice about attacking the Hidden Leaf with Minato and Kushina back. And Naruto could focus more on building a family and passing on his own legacy with his parents' guidance.
On a personal level, Naruto would finally get the family he always wanted. But it might also bring some confusion and adjustment issues. His parents would be from a different time, and they'd need to adapt to the new world Naruto lives in. For example, they might be shocked by the new technology and the changes in ninja warfare.
In some fanfictions, Naruto's father might be depicted as having an even more heroic past before his sacrifice. Maybe he had secret missions that shaped Konoha's future. For Sakura's parents, they could be shown as having high expectations for Sakura from a young age, which influenced her studious nature. For example, her mother might have been a medic - nin herself and passed on her knowledge and determination to Sakura.
Well, in fanfic, Naruto's father may be portrayed as a very passionate man. He was passionate about his village, his friends, and his family. His passion is what drove him to make the ultimate sacrifice. As for Sakura's parents, they could be seen as traditional. They adhered to the old ways of the village and expected Sakura to do the same. This made Sakura strive to fit into the village's norms while also trying to break free and be her own person.
Well, a common reason in fanfic could be that his parents are on a top - secret mission. This mission is so crucial and dangerous that they can't take Naruto with them. They have to sacrifice being with their son to fulfill their duties for the greater good of the ninja world.