Another motive might be related to some dark power corrupting Team 7. This power could have twisted their minds and made them see Kakashi as an obstacle in their path to achieving ultimate power. It could be something like the curse mark in the original Naruto series but even more powerful and insidious.
It could also be a result of a time - travel or alternate universe scenario. In this different reality, Kakashi might have made different choices that led to him being on the wrong side of Team 7. For instance, if he had been forced to work for a powerful villain in this AU, Team 7 might have seen it as their duty to take him out.
One possible motive could be mind control. Maybe an enemy manages to take over Kakashi's mind and forces him to harm Naruto. Another could be a misunderstanding. For example, if Naruto was thought to be possessed by a powerful and dangerous entity that Kakashi believed could only be stopped by killing Naruto.
One possible motive could be a dark magic or mind - control situation. Maybe an enemy has the power to control Naruto's actions and forces him to kill Sasuke against his will. Another could be a miscommunication where Naruto believes Sasuke has done something unforgivable, like harming the village in a way that Naruto can't overlook.
One possible motive could be a dark or alternate universe take. Maybe in this fanfic's world, there is some sort of dark magic or mind control that forces Naruto to do it against his will.
One possible motive could be if Sasuke goes too far in his pursuit of power and becomes a threat to the entire ninja world that even Naruto can't reason with. Maybe Sasuke starts to kill innocent people without hesitation, and Naruto, as the protector of the village and the one who believes in peace, sees no other option but to stop him by killing. Another motive could be some kind of dark magic or mind control that makes Sasuke an uncontrollable force of destruction, forcing Naruto to take drastic measures.
A possible motive could be that Naruto discovers some dark secret about Minato that makes him feel betrayed. For example, if he finds out that Minato was involved in some unethical experiments that led to the suffering of many people. Or perhaps Naruto is tricked by a powerful villain who manipulates his emotions and convinces him that Minato is the root of all his problems.
One possible motive could be power. In some fanfics, Sasuke might be driven by an insatiable thirst for power and see Naruto as an obstacle. Another could be revenge, perhaps believing Naruto has wronged him in some way in that alternate story. Or it could be a matter of being corrupted by dark forces, which make him turn against Naruto.
One possible motive could be to help Naruto control the Nine - Tails' chakra better. Hypnosis might be a way to reach into Naruto's subconscious and find a way to coexist with the powerful force inside him.
It could also be related to a prophecy or a pre - determined fate in the fanfic's plot. There might be some kind of dark prophecy that says Kawaki has to kill Naruto to prevent a greater evil. Or perhaps Kawaki is being controlled by an external force that has a vendetta against Naruto and uses Kawaki as a tool to carry out the murder.
Well, it could be that Kakashi is under some sort of dark spell or curse that makes him see Naruto as a threat to the village. In some fanfictions, there might be a situation where the village's safety is at stake and Kakashi believes that sacrificing Naruto is the only way to save everyone. Also, it could be a case of false information. If someone convinces Kakashi that Naruto has turned evil and is about to cause great harm, he might take the drastic step.
One possible motive could be a complete breakdown of the peace they had worked so hard to build. Maybe an outside force manipulates Gaara's mind, causing him to turn on Naruto. Another could be extreme jealousy over Naruto's popularity or power.