One reason could be that they come from different backgrounds in the fanfiction. This difference might create a barrier that prevents John from loving Sam. For instance, if John is from a very traditional family and Sam has a very radical lifestyle, John may be put off.
It's possible that in the fanfiction, John simply doesn't find Sam physically or mentally attractive. Physical attraction can play a role in the development of love, and if Sam doesn't meet John's standards in that regard, it could lead to John not loving him. Mentally, if Sam's ideas and views are constantly at odds with John's, that too can prevent love from blossoming.
One possible reason is that the fanfiction distorts the original relationship between Bella and Sam in a way she finds unacceptable. For instance, if it creates a false romantic tension where there shouldn't be one.
In some fanfictions, it could be a miscommunication situation. Sam might think he's doing the right thing in a hunt, but John disagrees. So, John spanks Sam not just as a punishment but also as a way to make him see his perspective. Also, it could be related to Sam's relationship with the supernatural side of himself. John might be trying to keep Sam's human side dominant by using this rather extreme form of discipline.
One reason could be that the fanfic focuses on a different pairing for Lucy. So, to make that other relationship more plausible, the author made Lucy not have feelings for Natsu.
One reason could be the sense of power it gives them. Trampling a man can be a very physical display of dominance. It makes them feel in control.
One common reason is over - exertion. Sam often pushes himself to the limit when it comes to fighting demons or saving people. His body can't always handle the stress and he collapses. For example, in some fanfics he might use too much of his psychic powers without proper rest, leading to a collapse.
Well, in the fanfiction context, Naruto may not love Sakura because he has unrequited feelings for someone else. Maybe he has a deep connection with another character that makes him view Sakura just as a teammate. Also, their personalities might not be as compatible in a romantic sense as one would initially think. Naruto is often impulsive and headstrong, while Sakura can be a bit more reserved in some ways, and this could lead to a lack of romantic attraction.
One possible reason could be that Renesmee simply has different interests. Maybe she is more drawn to a different lifestyle or set of values that Jacob doesn't align with. For example, she might be interested in exploring the world in a more solitary way while Jacob is more about the pack and community.
It could be due to a misunderstanding. For example, Percy might have done something that Annabeth misinterpreted as betrayal or insensitivity. This could have led to her feelings changing or fading away in the fanfiction.
The rich cultural heritage depicted in Marathi novels is a major draw. They often showcase unique Marathi traditions, values, and ways of life.
Maybe John has different values from Sam in the fanfiction. Their personalities or goals might be so different that John can't develop feelings of love for Sam.