We can't really apply new rules to existing conditions ... suffice it to say that such attempts in the past led to such injustice that out very Constitution specifically forbids 'ex poste facto' laws.
Perhaps it is believed that time, and attrition, will eventually see all the bad old stuff replaced. Or, it is felt that there is sufficient growth in our future that the percentage of old stuff will dramatically decline.
Maybe, even, some code wonk went on a British holiday, and was inspired by their use of these receptacles - and just couldn't wait to bring the idea home with him.
Whether the manufacturers were behind the proposal or not, you can be sure that the prospect of replacing their sales of 50 cent devices with 5 dollar ones did not cause them to cry out in despair!
Personally, I believe that the NEC departed from the 'minimum' standard long ago, and has adopted a proactive 'if it saves one life' approach. That such an approach is patently self-contradictory is besides the point .... critical thinking and honest discussion seem to be endangered species these days.
Just keep your eye on the ball: this, and other changes, have no effect until adopted by your local AHJ. Much as the NFPA would like you to believe that the NEC is the 'bedrock' of our codes, the actual fact is that hardly any jurisdiction adopts the NEC without some modification. Now is the time to act - if you want to stop this rule.
