Jamie Lloyd’s arc in the Halloween franchise came to an end very early on in Halloween: The Curse of Michael Myers, and there were mostly narrative reasons behind it. Halloween: The Curse of Michael Myers is the sixth installment in the franchise, which went beyond and above and added new elements to the Michael Myers mythology that didn’t appeal to fans, making it one of the lowest-grossing entries.
The Curse of Michael Myers (or Halloween 6) follows the events in Halloween 5: The Revenge of Michael Myers, where at the end Jamie Lloyd (Laurie Strode’s daughter, played by Danielle Harris) was seen hiding inside the police station after a “Man in Black” killed the officers and let Michael Myers free. In Halloween 6, audiences learned that this man abducted both Jamie and Michael, and kept them captive for years. Things got even weirder for Jamie after that, who didn’t even make it to the end of the film this time.
In Halloween 6, Jamie (now played by J.C Brandy) is impregnated and gives birth to a baby boy the day before Halloween, but the “Man in Black” takes the baby away. Jamie escapes with her baby but is quickly found by Michael Myers. At a bus station, Jamie hides her baby and escapes back to her truck. As she drives away, Michael forces her to crash into a farm, where she runs to hide. Michael finds her and impales her on a corn thresher – you can imagine the scene. Her baby is later found by Tommy Doyle (played by Paul Rudd), the boy Laurie babysat on the first film, and some crazy revelations are made. Jamie’s death early in the film was necessary for the story to continue and for the development of new, mystical details about Michael’s evil nature.
Later on, it's revealed that Michael is believed to have been inflicted with an ancient Druid curse named Thorn. According to the tradition of the cult, the child chosen to bear the curse must sacrifice its next of kin on the night of Halloween, meaning that Jamie’s son should be Michael’s sacrifice, as he’s his niece’s baby. The “Man in Black” that abducted Jamie is actually the leader of the cult, and there was no way he was going to let Jamie escape with the child, so her death was necessary – that way, Michael’s cycle of evil could continue.
Danielle Harris wanted to reprise her role as Jamie Lloyd in Halloween 6, but the producers reportedly refused to pay her the amount she requested (and she didn’t like the script either), and replaced her with J.C Brandy. The studio didn't want Jamie Lloyd around anymore after giving birth, with early versions of the script having her fall into a coma after being attacked by Michael, only to be killed by Dr. Terence Wynn (the “Man In Black”) at the hospital.
Jamie Lloyd was created after Jamie Lee Curtis refused to reprise her role as Laurie Strode for Halloween 4. With the franchise slowly but surely decreasing in quality and viewer’s interest in it fading away, Jamie’s death in Halloween 6 was meant to be, not only because she was an obstacle for other characters, but because her character wasn’t relevant or appealing anymore, so much that she was completely erased from canon in Halloween H20: 20 Years Later and in the latest reboot.