It's actually quite logical. The suit modules are supposed to be connected and disconnected serially, except in medical emergencies.
The de-catheterization is accomplished via helmet controls, but the codplate and loin-joiners won't pop off until after the helmet is removed.
Can't we classify "I don't want to pee in a catheter" as a medical emergency?
I guess that depends on whether anybody's shooting at you when you want to pee.