They don't know that the soloist got sick. They don't know that the band performed the show better last week. They don't know what special adversity your band overcame. If they knew, they might be even more impressed than you are. But they don't know.
Judges detect small mistakes.
Judges have the training and experience to detect tiny problems with intonation, tone quality, balance, ensemble, etc. These subtleties aren't even noticed by normal people. These small differences separate the very very good from the merely very good. Just because these differences are tiny does not mean that they are not real. Contests that give rankings usually use forced rankings.