In junior high school, sometimes I can come up with a different solution to a math problem, which many people can't figure out, but why didn't I do well in the exam?
Judging from your description, your thinking is good, especially divergent thinking. But as far as the exam is concerned, you need very strong ability, solid basic knowledge, careful thinking, good computing ability, reading ability and so on. The poor test may be due to the lack of systematic study, solid basic knowledge and weak ability to take exams.