As a brass player, I find myself wondering.

Why does ANYONE march bass clarinets?

They're nearly inaudible on the field, unless amplified, unless you have a half dozen or more of them being played. They're cranky, high-maintenance, and delicate instruments.

What purpose does it serve a band to have a kid march with that instrument? Why not put your BC players on soprano during marching season? Or let them learn to double on tenor saxophone?