Fair enough, but it can be any reason. Hell, the time travel rules could have that a person can only travel back in time if they didn't
already exist in that time period.
Ultimately, the writers will tell the story they think is the best story. But there's no inherent reason it couldn't be Kitty Pryde or had to be Logan. Ultimately, it came down to what story they wanted to tell and the rules of time travel accommodate that story.