Maybe it's to create more tension and emotional depth in the fanfiction. Pregnancy often brings a lot of changes and challenges that can drive the plot forward.
Well, sometimes in fanfiction, writers take liberties to create unexpected plotlines. Maybe this pregnancy was a way to bring a fresh perspective or add more layers to the story of Hannah and Bryce.
In 13 Reasons Why fanfiction, Hannah could be depicted with a stronger determination to overcome her past or might have new relationships that shape her differently. Also, her character development could take unexpected turns.
Zach stopping Hannah could be due to a variety of factors. Maybe he was scared of the consequences of their interaction or was dealing with his own internal struggles that made him act that way. It's possible that new information came to light that made him change his mind about supporting her.
The possibilities are endless in fanfiction. Hannah could be haunted by her past, have new relationships in the afterlife, or even become a spirit trying to help others. It all depends on the creativity of the writer.
Often, fans feel a connection to Clay and Hannah and want to create their own versions of what could have happened. Fanfiction gives them the creative freedom to do that. Maybe they think the show left some room for imagination or they have their own ideas about how the characters' lives could unfold.