The most obvious reason to off Wolverine is that Logan will be the last time Hugh Jackman plays the character.
Whether you liked Jackman’s portrayal of Wolverine or had issues with it, there’s no denying that he popularized the character for an entire generation, so it would be fitting it the character passes onto the great beyond as Jackman departs.
After all, just because Jackman is retiring the character doesn’t mean that someone else can’t take over.
Now some you you may reasonably ask why the franchise doesn’t simply recast someone else in the role?