We all have our musical preferences (and exceptions) when it comes to setup and quality, but all in all, the judges know skillful music when they hear it. They have knowledge as well as natural inclination; they know "good" when they hear it. Also, no one's getting any profits off of what's being heard so it's definitely more about the music.
I don't think that bias is bad in every sense. In fact it can be good. Are we speaking of quality or genre?
The judges seem to listen a song itself: the idea (a creative idea), the "hype" of a familiar mix (everyone likes to hear a redo of a song they really love), vibe (the mood and setting of a song; what it's good for), arrangement (chorus, break, verse, abstract, etc), composition (chords, melodies, harmonies, countermelodies, arpeggios, velocity, accent, reciprocity, etc), and whatever else you could name.
As long as the judges are familiar with almost or all kinds of music, I'm cool. I don't care if it's engineered, acoustic or both, good is good and garbage is garbage.