what a stupid question lol. i doubt there is a specific reason why dru down isnt rapping on all about you. i imagine the track was done pretty much and dru down was in the studio and he went in and laid down the part he did on the track and they decided it sounded tight. maybe an impulsive thing as a sub-sequent result of lots of liqour and ganja. do you think tupac sat down and decided who were gonna be on a track and a specific reason why they should be on the track every time he recorded a track? i mean, what do you expect us to tell you? that jupiter was blocking the sun from reaching one of pluto's moons, and that's why dru down didn't rap on the song? who fucking knows.