The JJBA manga is indeed finished. It had a great journey and wrapped up with a satisfying conclusion for fans. However, there's always the possibility of spin-offs or related works in the future.
There could be multiple factors. His role models, whether they were his teachers, older siblings, or people he read about in books, might have inspired him. Also, the realization that hard work brings rewards, like good grades, praise from others, and a sense of accomplishment, would have made him keep up his hardworking attitude.
Rohan was a boy who always put in great effort in everything he did. He woke up early every morning to study before school. He was dedicated to his schoolwork, always completing his assignments on time and with high quality. He also helped his parents around the house, doing chores without being asked. His hard work paid off as he got excellent grades and was respected by his teachers and peers.
One common theme is the exploration of their complex relationship. Given their different personalities in the original series, fanfictions often delve into how they interact and come to understand each other better. For example, Josuke's more easy - going nature contrasted with Rohan's often - prickly demeanor.
There's also 'Diamond in the Rough'. This fanfic focuses on a unique relationship between the reader and a JJBA character. The writing style is very descriptive, especially when it comes to the Stand battles. It really brings the action to life and makes you feel like you're in the middle of the chaos.
Some JJBA fanfics that are worth reading are the ones that expand on the battles. They might add more complex strategies or new foes that the characters have to face. For instance, a fanfic could introduce a new stand user who has the power to manipulate time in a different way than Dio. Also, fanfics that give a different perspective on the existing story arcs, like seeing the events of Stardust Crusaders from an enemy's point of view, can be quite engaging.