* Lack of ambition: Homer generally lacks the ambition to pursue higher education. He's content (or at least accepts) his role as a low-skilled worker at the nuclear power plant. Finishing high school would require effort and commitment, neither of which consistently motivates him.
* Fear of failure: Homer's history of poor academic performance and general ineptitude might lead him to fear the challenge of returning to school and potentially failing again. This fear might be subconscious.
* Aversion to authority: School represents authority, rules, and structure, all things Homer frequently rebels against. The idea of being subjected to teachers and curriculums could be a significant deterrent.
* Short-term gain over long-term benefit: Homer prioritizes immediate pleasures and avoids anything requiring sustained effort. Finishing high school offers a long-term benefit (potentially better job prospects), which holds little appeal compared to immediate gratification.
It's important to remember that Homer's lack of a high school diploma is a defining characteristic of his comedic persona. The show doesn't offer a deep, psychologically-driven explanation for his educational shortcomings; rather, it uses it as a source of humor and to highlight his flawed, yet endearing, personality.