One word answer - inertia. Many (most?) rule changes are rushed through in response to a perceived need (then sometimes revised as problems with the original rush-jobs are recognized). Rules which may no longer required but doesn't cause any significant problems (when was the last time anyone was penalized for violating t53.3?) aren't likely to rise to that level of concern. That being said, there is hope - it was only a couple of years ago that the requirement for the extremities of the grip to be insulated in foil was dropped (a rule intended to help prevent grounding of the weapon to the lame), so apparently someone is aware that grounding of weapons against lames is no longer the problem that it once was.