Because, from a common law perspective (and remember that the Constitution is essentially a formalized, codified form of common law), there is no obligation to 'register' one's vehicle if it is being used for non-commercial use on a public road.
The 'requirement' for people to register their vehicles and indeed, obtain a driver's license, is part of the scam and fake 'color of law' that has been perpetrated over the past 100+ years, in many parts of the world.
Because, from a common law perspective (and remember that the Constitution is essentially a formalized, codified form of common law), there is no obligation to 'register' one's vehicle if it is being used for non-commercial use on a public road.
The 'requirement' for people to register their vehicles and indeed, obtain a driver's license, is part of the scam and fake 'color of law' that has been perpetrated over the past 100+ years, in many parts of the world.