She could be seeking some form of connection. Elena has also been through a lot in the vampire - filled world. Rebekah might see a kindred spirit in Elena and believe that sharing her story will create a bond between them. It's also possible that Rebekah is lonely and just wants someone to listen to her long - held secrets and experiences.
Another reason could be strategic. By telling Elena her story, she can influence Elena's decisions. Maybe she wants Elena to side with her in some upcoming conflict. Rebekah knows that Elena has power and influence among the other vampires and humans, so by sharing her story, she hopes to gain Elena's trust and support.
Perhaps she wants Elena to understand her better. Rebekah may feel that Elena has misjudged her in the past, and by sharing her story, she can show Elena her true self.
She might want to manipulate Elena. Katherine is known for her devious ways, and by sharing her story, she could be trying to gain Elena's trust or sympathy for her own purposes.
To help Hope relax and fall asleep easily.
She might want to inspire others. If she has gone through a tough situation like beating an addiction, by sharing her story, she can give hope to those who are currently struggling with the same problem.
She might want to preserve her family's heritage. By sharing the story, she ensures that the family's unique experiences and values are not forgotten.
I really like 'Elena and Rebekah: A New Alliance'. In this fanfiction, an outside threat forces them to team up. The author does a wonderful job of exploring their different strengths and how they complement each other in the face of danger.
Maybe it involves her family history, like her relationship with her siblings. Rebekah might talk about the old days, their powers, and the feuds within the family.
Maybe it's because similar themes or plot elements are common in many stories, and you've encountered them before.
A common plotline is them competing for the same guy, which leads to a lot of tension and interesting character development. For example, in some fanfics, they both have feelings for Damon, and this rivalry makes for a very engaging read.
Maybe he sees something in Naruto that makes him want to share. Naruto has a strong belief in peace that might make Nagato feel like he should explain his own actions and past.
Maybe it's a fairy - tale about a brave princess and a magical dragon.