I was playing some contrabass clarinet parts and wondered why there are so many passages where every single bass instrument is playing, minus the contrabass clarinet. The bass clarinet, tuba, and stringed bass are also playing, so I don't know why the contrabass clarinet would be excluded, especially if it is playing in the same octave as the other basses.
For example, at bar 248 of Alfred Reed's "El Camino Real", the bass line is being played by all bass instruments (minus bassoon, which is being used for something else), except for contrabass clarinet:
Even the contrabassoon is playing along.
There are also points where only tuba and stringed bass play the bass line. What about those two instruments makes it so special for playing bass lines, and why aren't those parts also given to low woodwinds?