There are a lot of cars that were maintainable, and built to be maintained, that can’t be maintained anymore simply because the manufacturer went defunct and there are no more parts (e.g. Saab, Datsun) or because the cost of manufacturing more parts for a car with a dwindling owner-base began to outweigh the profit, and thus, there are no more parts (e.g. older Ford models).

Unless the car is built primarily with 3rd-party parts (from manufacturers like Bosch, Brembo, etc) - which is something that consumers usually hold against a car, like how many people are upset that the new Toyota Supra is actually a BMW - then the problem is almost completely analogous to the shutting down of remote servers; if the manufacturer goes defunct or can no longer make a profit by continuing service, the car’s life has perished.

And in fact, the only way to avoid this is super conglomerates and monopolies - Lamborghini parts should always be available, because they come from the Audi parts bin, which comes from the Volkswagen parts bin.