Disinfecting every nook and cranny of the thing is a herculean task.
The inside of the rear compartment has these little crevices where the
mildew is growing.  They're hard to reach and hard to clean.  Just like
the nooks and crannies on the front.  You can't  just wipe the whole
thing down with a towel; you have to stick a toothbrush or other small
brush inside each of those little crevices and scrub each individually.

A device intended to be used in a moist environment shouldn't have
hard-to-clean nooks and crannies.

Steven,
 My husband is a dentist, and he gets articles that advise him that
there are biofilm matrixes forming in the tubing of his dental
equipment: after he showed me one article, I started to boil my neti
water. He uses "shock" to clean his lines--I think it's beach based.
 So, even if you clean the mold off the outside: what's on the
inside?
 Because he's a dentist, we have these electric toothbrushes, and the
original Braun design encouraged absolutely disgusting growth, that
was hard to clean, around the brush holders. The newest model, just
has a simple base, but weekly, it grows green slime--likely
pseudomonas.
 You're right: anything that uses water has to be designed to
discourage water loving bugs, or be easily cleaned.
  I toss my neti pot in the dishwasher on the sanitizing cycle, and I
use vinegar in the NeilMed.
Judy