In some fanfictions, his parents might be forced to abandon him due to a powerful enemy threatening their family. They may believe that by leaving Naruto alone, the enemy will not target him immediately, thinking he's just an ordinary orphan.
In fanfiction, his alive parents could abandon Harry due to a prophecy. They might have been told that Harry was destined for great evil or something terrible was going to happen because of him. So, in a misguided attempt to prevent this, they abandoned him. Or perhaps they were under some kind of dark magic influence that made them believe that Harry was a danger to them or the wizarding world, even though it was all false.
In some fanfics, they might abandon Harry because they are under a dark spell. This spell could make them lose their love for him and force them to leave. Another reason could be that they are blackmailed by some powerful dark forces. These forces may threaten their lives if they don't abandon Harry.
One possible reason could be jealousy. Maybe Naruto has achieved something great and his friends are envious. Another reason might be a misunderstanding. There could have been some false rumors or misinterpretations of Naruto's actions that led his friends to believe he wasn't trustworthy or a good friend.
Maybe she was forced to for some dark reason. Perhaps there was a threat to Naruto's life if she stayed, and she thought leaving was the only way to protect him.
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.
In this fanfiction, it could be that Naruto's parents were under some sort of mind - control. Some evil entity could have taken over their minds and made them feel hatred towards Naruto. Also, it might be related to a family secret or feud. There could be something in the family's past that made them believe Naruto was a stain on their family name, even though Naruto himself was innocent. It could also be a case of false information being spread around the village which made his parents believe lies about him.
His life could become very difficult. He might have to fend for himself at a very young age. Maybe he has to live on the streets, stealing food just to survive.
It could be that they were misled. For example, they might have been tricked into believing that Naruto was a threat to the village in the future. So, in an attempt to safeguard the village they love, they decided to 'betray' Naruto. This would add a lot of complexity to the story as Naruto discovers the truth later.