>That makes sense to me because for musicians, hearing just the music still makes your brain want to focus on the structure of it, time signature, rhythm patterns, interesting chords, key changes, etc

There's special music for focus that tries to keep all those to a minimum. 4/4 beats, no fancy rhythms, no changes, basic chords and repeating melodies etc. After a while, even if you're Mozart, you can ignore it just fine, just get the vibe and the driving pulse.