Because during the flashback where Luke was training her, the twins were still young, and it is very likely that Ben had not been born at that point. By having Leia end her Jedi training to focus on being a mother, it would make sense to lay down her lessons from Luke. It also makes it seem Ben chose to die rather than it being destined to be.
What if…
Luke: “It was the last night of her training. Leia told me that she had sensed the
death of her son at theend of her Jedi path. She surrendered her saber to me and said that one day… it would be picked up again… by someone who would finish her journey. We’ll always be with you, but this is your fight.”Leia quits being a Jedi, because as it has been explained numerous times, she never wanted to be one. Leia wanted to focus on politics and then dumped her son on Luke later on to train. What if we just make that line about Leia realizing that, being a Jedi is not for her, and someone else would eventually take her spot. In my opinion, it makes her taking on Rey as a trainee even stronger as she believes Rey would be her successor as a Jedi. Just food for thought!
You know what, that could actually work.