There're many different vendors of karaoke.
In a multitrack, you get an opportunity to transpose every track separately: signal interpenetration will be lower; the level of noise will decrease in accumulating signals.
The reason is not in that scientists do not think about musicians, the reason is that the music has a very complex physical and psychological nature, perception of music is grounded on some psychoacoustic phenomena, and all these things are interwoven into our concept, and poorly formalized.
The difference is that all instruments are bounced in a stereo-track.
The format is the most common and the most popular.
One bad move can destroy a whole mixdown! Oh yeah yeah Oh yeah yeah yeah Ooh! We do that a lot.