Another reason could be his search for a cure. Bruce may leave the Avengers in fanfic to focus solely on finding a way to permanently separate himself from the Hulk. He might feel that the team environment is not conducive to his research and that he needs to be on his own to make progress.
One common theme is the exploration of their unspoken attraction. They both are complex characters and fanfics often play with how they might come to terms with their feelings for each other.
One possible reason could be a difference in ideology. Maybe Spider - Man has a more local - friendly approach to crime - fighting while the Avengers are often involved in large - scale, global threats. He might feel that his skills are better utilized in his own neighborhood, like Queens, rather than in the grand, often cosmos - level battles of the Avengers.
One reason could be to seek a new life away from the political drama in Konoha. Naruto has always been in the spotlight and has faced many political challenges. Hinata, being by his side, might support his decision to leave for a quieter place. Maybe they want to raise their family in a more peaceful environment, away from the constant threat of enemies targeting Konoha.
One reason could be that Bruce is being too reckless in the fanfic. Alfred has always been there to keep Bruce safe and if Bruce is constantly putting himself in unnecessary danger as Batman, Alfred would be disappointed. For instance, if he jumps into a fight without proper preparation or a well - thought - out strategy.
It could be to introduce unexpected plot twists and keep readers on their toes. Maybe a character has to leave for personal growth or to create tension.
One common theme is his struggle with the Hulk. Writers often explore how he copes with this dual identity, like in stories where he tries to find a permanent cure. Another theme is his relationships, especially his friendship with the other Avengers. For example, how Tony Stark might help him with his scientific research related to the Hulk.
One possible reason could be that Bruce is being too reckless in his Batman activities. Alfred, being the caretaker, might see Bruce endangering himself unnecessarily and decides to punish him to make him more cautious.
Characterization. If it really nails Bruce's complex personality, it stands out. For example, showing his intelligence as a scientist and his insecurities about the Hulk.
Yes, it could be a must - read. Fanfics about Bruce in the Avengers universe can offer unique perspectives. They might explore his character deeper, like his internal struggles with the Hulk. It could also show different relationships within the Avengers team from his point of view.
It could also be due to emotional turmoil. Tony has lost a lot in his life, like his parents and some of his friends. In the fanfic, if he was faced with a situation that reminded him of those losses or if he had a falling - out with a close ally like Pepper or Rhodey, the emotional shock could be so great that he collapses. He's a man who often keeps his emotions bottled up, and when they finally break through, it could have a physical manifestation like a collapse.