It was not a deliberate oversight
But, it was deliberately not done
The random pitching is applied in MMA.pat.sendNote(). This routine is used by all tracks, except for plectrum. Why? Plectrum notes do not have a duration (all other track notes do). So, a special routine is contained in patPlectrum.trackBar() to send notes to the midi machine. Note that this code is also responsible for tracking the current state of the notes already playing.
I _think_ this could be added to plectrum fairly easily by inserting a call to MMA.rpitch.doRpitch() (refer to the sentNote() code to see how). You'd need this in fretboardNotes() and fretboardShapes().
If you're up to it ... have a go. In the meantime I'll make a doc note that it doesn't work for plectrum tracks