Because it might not be possible.
Classifying it as a new type might mean every part has to meet 2020 rules and regulations.
It's really a problem with all the certifications, FCC and FDA aswell as FAA. The rules are so strict that the only way is to work around them. So the response to this is to make the rules more strict.
I have had it happen with old university buildings. We couldn't add a fire alarm because it would trigger a new fire plan, which would mean new fire exits, disabled access, improved insulation standards etc etc. Adding a small amount of safety to an old high fire building is impossible because of all the new safety rules.