Your logic presumes that the documentation needs to expire, when the question was why you see value in it expiring at all. There is no reason for annual auto registration expiration either, other than to collect the fee.
Those agencies that register/document boats, cars, trailers, trucks, motorcycles, airplanes, etc. will eventually become overwhelmed with records of vehicles that no longer exist, have been abandoned, sold out of their jurisdiction, etc. People are good at getting things registered as there are consequences of not doing it, but having vehicles de-registered just ain't going to happen.