Where was Mark Arm?

Evil Chris

A thought occurred to me while watching PJ20. Mark Arm was part of the initial Green River group, there's references to him in PJ20, tee's of Mudhoney all over the place, etc..

But he gets no screen time, no lines at all in the movie. Anyone know why?
He would surely have been able to give some nice insight into the infancy of the band(s) back in the earliest of days of the Seattle scene.