One possibility could be that there's been some sort of magical interference. Maybe a dark wizard has cast a spell to disrupt the owl post. Another reason could be that the wizarding world is in chaos and the postal system has broken down.
It can create a sense of isolation for the characters. Without letters, they are cut off from their usual sources of information and support, which can make them more vulnerable.
In fanfiction, Harry Potter rejection letters can be a fascinating aspect. They might be letters rejecting Harry from certain opportunities within the wizarding world. For example, he could be rejected from a special magical club or a scholarship. These rejection letters add depth to the story by showing that even the 'Chosen One' isn't immune to setbacks.
In some fanfiction, you might find letters from Harry to Sirius that are full of his thoughts about Hogwarts life. These letters often express his concerns about Voldemort's return in a more personal way than in the original books.
He could work at Weasleys' Wizard Wheezes. He has a good relationship with the Weasley family, and it would be a fun place for him to work, helping with inventing and selling all kinds of magical pranks and toys.
Hagrid could be a great help. He has a lot of connections in the wizarding world, especially with those related to magical creatures. He might introduce Harry to someone who needs help with taking care of or studying magical beasts, and thus get Harry a job in that area.
One common theme is the idea of being an outsider. Harry already feels like an outsider in the wizarding world at times, and a rejection letter can emphasize this. Another theme could be unfairness. The letter might be a result of some sort of prejudice or misinformation within the wizarding community.
The letters can act as a means of communication between characters who are separated. For instance, when Harry is on a mission away from Hogwarts, a letter from Hermione might contain crucial information or advice that helps him in his task, thus driving the plot forward.
Letters often serve as a means of communication between characters in different locations. In fanfiction, they can carry important plot - driving information. For example, a letter from Dumbledore could reveal a hidden prophecy that sets the course of the story.
One great 'Harry Potter' fanfic about letters could be where the Hogwarts letters are intercepted by dark forces and the story follows how the wizarding world copes with it. For example, it might lead to a secret mission by the Order of the Phoenix to re - send the letters to the Muggle - borns.