After a turbulent three seasons, Minka Kelly’s Lyla Garrity left Friday Night Lights as that was what was best for her character. Lyla Garrity, the daughter of Buddy and Pam Garrity and girlfriend to Jason Street, is one of the original main cast that started the show. Her official exit at the beginning of season 4 follows the exit of other main characters Jason Street, Tyra Collette, and Brian Williams as well.
Throughout her first two seasons, Lyla’s story revolves around her faith and her interest in both Jason and Tim. In the first season, Lyla and Jason’s relationship is rocky after Jason’s accident that puts him in a wheelchair. Additionally, her parent’s divorce and her father’s affair put a strain on her, and she ends up quitting cheerleading and attempting to find herself. By the beginning of Friday Night Lights season 2, Lyla has refound her faith and spends the season working with Christian ministries. In the end, she ends up back with Tim, having made peace with Jason over their relationship.
Actress Minka Kelly, who won't return for the Friday Night Lights reboot, ultimately made the decision to leave, causing Lyla's departure from the show's main cast. For Minka, it was time to move on, and she felt that it was the best decision for Lyla Garrity to not stay on the show after graduating from high school. It simply made more sense storyline-wise to allow the character to move on from the show. The character likely would have been moved from the main cast anyways as the show was focused on the high school students, and other characters had also graduated and moved away from Dillon in the same way.
While Lyla officially doesn't leave until Friday Night Lights season 4, she struggles with her decision to leave the show throughout season 3. In Friday Night Lights season 3, Lyla Garrity struggles to decide between her boyfriend Tim Riggins and her dream school, Vanderbilt. Attending Vanderbilt meant that she would have to move far from Dillon, Texas, which actively countered Tim's contentedness in staying in Dillon. Originally, she decides to commit to San Antonio State University, giving up her dream school to stay with her boyfriend, and when her father loses her entire college fund, she feels as though she has no choice. However, by the end of the season, she's able to afford Vanderbilt, and she takes the opportunity to leave Dillon and head to Nashville. This development concluded Lyla's arc organically, making her departure seem all the more natural.
Minka Kelly did return as Lyla Garrity as a guest star for the second episode in season 4. Lyla returns from college briefly for Matt's father's funeral, and she and Tim rekindle their relationship. Despite both realizing they still have feelings for each other, Lyla stays firm in her decision to stay at Vanderbilt, and she leaves Friday Night Lights main cast for good. In the end, it was likely best for Minka Kelly's Lyla Garrity to leave Friday Night Lights, as her exit was more true to the realistic experience high schoolers have after graduating and leaving their hometown, ultimately adding to the show's authenticity, and was best for her character.