Thor was in a very bad place in Avengers: Endgame. While he started out as a very angry God of Thunder, after he chopped off Thanos' head, he ended up regressing, becoming depressed and letting himself go as he sat around drinking mead and playing video games.
Thor's regression from the self-assured warrior into someone who just wanted to sit on the couch and do nothing is why he met his mother Frigga when he traveled back in time, notably not having a moment with Jane Foster.
Thor had a ton of problems in Avengers: Endgame, but girl trouble was not one of them. In Thor: Ragnarok, viewers learned that Thor and Jane were no longer dating and that was the end of that. In Avengers: Endgame, they needed to get the Aether from Jane, but it was Rocket who did it instead of Thor.
According to co-writers Stephen McFeely and Christopher Markus, there was no reason to add girl troubles to the rest of Thor's problems. Markus said in an interview with Empire that it was also important not to add Odin to the story because the last thing the MCU needed was "more father issues."
Thor was a mess and had no direction, and when someone is in that bad of shape, they need their mother. Since Thor's mom died shortly after the moment they arrived in the past, this was his only -- and last -- chance to get to speak to Frigga again. As a good mother would, Frigga told Thor exactly what he needed to hear to become a warrior once again -- bluntly, but with love.
“He had some Jane Foster time in one draft," Markus said. "But that didn't seem like his issue. He's reduced to a childlike state in his cabin over there in Norway, and he needed advice from his mom, basically. Someone needs to go, 'You're OK. You're a f--- up, and you're OK.”
Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr. as Iron Man, Chris Evans as Captain America, Mark Ruffalo as Bruce Banner, Chris Hemsworth as Thor, Scarlett Johansson as Black Widow, Jeremy Renner as Hawkeye, Brie Larson as Captain Marvel, Paul Rudd as Ant-Man, Don Cheadle as War Machine, Karen Gillan as Nebula, Danai Gurira as Okoye and Bradley Cooper as Rocket, with Gwyneth Paltrow Pepper Potts, Jon Favreau as Happy Hogan, Benedict Wong as Wong, Tessa Thompson as Valkyrie and Josh Brolin as Thanos. The film is in theaters now.