Logan spoils Rory the way a father spoils his little girl, giving everything he has and sometimes even irresponsibly.
She never had that growing up. She never had anyone to turn into when she’s mad at her mom. Lorelai was the only stable caregiver she had.
Although she’s a grown up now, and she knows she has to mature. I don’t think she could ever totally fill that void from childhood; it’s too big and intense.
So whenever she’s vulnerable, she’ll go back to Logan again and again only to get that nurturance and safety; then go back to the adult world and leave him again and again.
Kinda like the way Lorelai and Christopher get together every time they fight with their parents. Luke is the right one but he’ll never have the history and understanding those two have with each other.