Because when a project is done in 10 minutes by llm - it will be abandoned in a week.
When a person intentionally does it and spends a month or two - they far more likely will support it as they created this project with some intention in the first place.
I’d be willing to bet the classes of bugs introduced would be different for humans vs LLMs. You’d probably see fewer low level bugs (such as off-by-one bugs), but more cases where the business logic is incorrect or other higher concerns are incorrect.