I am thinking that Kylo killed Luke's wife along with the other young jedi similar to Darth Vader's path to the dark side. Luke drops off his daughter somewhere similar to where he grew up so Kylo can't find her. He would want to turn her to the dark side or kill her. If he left her with Leia she wouldn't have been hidden. Kylo can read almost anyone mind so he would find her. The only reason Rey resists is she actually seems stronger in the force.