There's not an in universe reason. It's the showrunners' choice, probably a creative decision. They wanted to introduce Luke Cage in her show, but felt no need to do it the other way around, or that she doesn't fit the story, or doesn't add anything to it - probably a combination of those reasons.
They ended up in good terms at the end of Jessica Jones. In the last 2 episodes, despite him being mind controlled by Kilgrave, she initially refuses to shoot him. He tried to fight it off and to avoid hurting her.
Jessica: Please stop. Please stop.
He had a painful expression on his face and seemed to fight, then said:
Luke: Do what you gotta do.
She shoots him, then try to get him help.
In his last scene of the show, after he wakes up, he finds out Jessica was arrested and wants to break her out.
Claire: She's been arrested. She killed someone. It's all over the news.
Luke: He got to her.
Claire: No, no, no. She got to him. Kilgrave is dead.
Luke: She did it.
Claire: Yeah, she did it.
Luke: They can lock her up for that. I won't let that happen.
Claire: Okay. Okay, enough. She saves you, you save her, then she has to save you again. And neither one of you want to be saved, right?
In The Defenders, when they meet again, he was trying to convince her to stay due to their past relationship. In the 6th episode, they briefly address why they didn't keep in touch:
Luke: I can't believe this is what it took for us to talk again.
Jessica: I'm not good at keeping in touch. But you could've called.
Luke: Fair enough.
