I keep thinking about this and how to explain it better. In certain types of music that rely on the button box (cajun, zydeco, tex-mex, tarantella, Irish, others) the rhythm is so important, as these styles are often dance music. The fact that you can change from C to G (for example) without moving your finger, and getting the percussive rythmic effect of the bellows change is HUGE! In fact, it can be argued that it is 92% of what gives it the drive and style. That's why the basses remain "mixed."