I don't have any interest in digging through those threads, either, or the time to do anyone's homework, but there's one thing I remember someone saying (I don't remember who said it, so it may just have been someone guessing at the motivations, not someone involved in making the decision).
The problem started when Nemesis established that Janeway had become an admiral. That meant she was no longer going to be part of a happy little Voyager gang, because she'd moved on. It'd be harder to come up with stories in which she had a legitimate reason to be part of the action along with the rest of the gang. So, if she was being effectively cut off from the other core characters, why not do something that cut her off from the characters and would generate some emotional and dramatic stories?