Same reasons as why things like Clipper Chips isn't happening. It completely lacks technical basis, and even political consensus gets sketchy quick.

Post-war Commonwealth nations are generally bad at gun designs as well - UK tried once and produced an infantry rifle that will(not could) seriously injure its user if held and fired in left hand. So even if forced, the approved gun will be more of a theoretical product, and the smart gun mandate will just be a less politically viable alternative to total firearms ban.