I'm pretty sure it wasn't Luke that left Rey on Jakku. Luke's expression when he sees Rey looks more to me like he thought she was dead and can't believe that she isn't, not "Oh crap... you found me!". During her vision, one of the Knights of Ren is about to attack her before being stabbed from behind by Kylo, who then walks towards her. It then cuts to her as a child on Jakku, watching a ship fly away. That, along with the fact that Kylo nearly kills a FO officer when he mentions that Finn and BB-8 escaped Jakku with "a girl"(and then demands, "WHAT GIRL?"), at least to me, suggests that Kylo is the one responsible for Rey being dropped on Jakku without her memory of her life before that, and a seemingly programmed directive to wait until a set of non-existent parents return for her. In the novel, it's also explicitly stated that Kylo knows WHO Rey is. I think the most likely scenario is that, for whatever reason(likely because there WAS still good in him at the time), Kylo could not bring himself to kill Rey during the massacre at Luke's Jedi academy. However, given how powerful Rey is in TFA, Kylo probably knew that he also couldn't just leave her for Luke to continue training. He also correctly assumed that if Rey was still alive, Snoke would sense that she was a more powerful candidate and would have replaced Kylo with her. In the novel, during the end of Rey's duel with Kylo, Rey hears a voice in her head(implied to be Snoke's) telling her to "Kill him!", but she resists it.