It could also be that the fanfiction is set in a universe where the circumstances just don't allow for him to be in a team. For example, the other superheroes might be too busy with their own problems in different parts of the world, or there could be some sort of political or social unrest that makes team - forming difficult or unfeasible. Peter then has no choice but to operate alone, and this gives the writer a chance to show how he copes in such a situation.
These fanfictions are appealing as they allow for more character development of Peter. Without the setback of being dusted, he can grow in different ways. For example, he might have been able to mentor new heroes or develop new powers. It also gives a chance to explore different relationships, like his relationship with the Avengers in a different context. It gives fans a chance to see a more complete version of Peter's story.
Maybe Peter Parker has his own distinct view of Steve. He might feel that fanfiction often distorts Steve's real character or the relationships in the original story, so he doesn't like it.
One great 'Peter Parker isn't dusted' fanfiction could be 'The Unbroken Spider'. In this fic, Peter continues his superhero duties without the interruption of being dusted. He has to face new villains that emerge during the time when others were snapped away. It shows his growth as a hero in a different timeline.
Peter will probably be very confused at first. He's used to being part of the team, and suddenly being hunted by them is a huge shock. He might try to talk to them to clear up any misunderstandings.
Peter's scientific mind would be an asset. He could work with the team's tech - savvy members. His superhuman strength and agility would also add to the team's combat capabilities. In terms of the team dynamic, he'd be like the little brother that everyone looks out for.
He might face more difficulties in fighting powerful villains. Without a team to back him up, he has to take on all the challenges alone. This could lead to him getting injured more often or having a harder time achieving victory.
Wanda Maximoff might be a key character too. Her powers were a big concern in the Sokovia Accords situation. Peter could tell her off for not being more careful with her powers and for getting involved in the conflict on Team Cap's side. Also, Clint Barton, Hawkeye, who came out of retirement to support Team Cap. Peter might criticize him for coming back into the fray and adding to the chaos instead of staying out of it.
Fanfiction might not be working because it doesn't connect with the intended audience. Maybe the pacing is off, or there are too many grammar mistakes that distract readers.
There could be several reasons. Maybe the pacing is off, making it feel too slow or too rushed. Or, it might not have a clear beginning, middle, and end. Also, if the author doesn't engage with the fan community and get feedback, it can struggle to succeed.
Maybe Peter simply doesn't like the idea of fanfiction that involves teams. It could be that he prefers original stories or fanfiction centered around individual characters rather than groups.