I would actually consider that a more significant reason this isn't done is due to billing confusion.
Over at Bell, trust me, we hate doing mobile number swaps...but we do them, as policy. But it sure creates billing confusion not only for the billing department, but for the users as well. I'm not sure about everyone else at Bell, but I seem to be the only person that understands them and how simple they really are...but even customer service reps manage to screw them up.
That could explain discouraging it or requiring a full explanation and consent from the customer about the risks and results, but if using lowest common denominator IQ or customer confusion as a reason would prevent them from performing many account changes that result in billing confusion. You are probably right, and I am sure this is the excuse they use internally.