Yes, because they make money selling the parts, and there are warranty requirements that are hard to fulfill if you don't have parts.

Often after a decade or so, companies will sell the designs to dedicated parts makers. For example, Volvo has Volvo Classic Parts, and they even have a reman program, and will even 3D print parts not available. Mercedes has Mercedes Classic Parts. Chrysler has MOPAR, etc.

Here you can browse parts for a 1968 Mercedes SEL: https://classicparts.mbusa.com/c-280sel-223

If you are a business, the costs of designing the part has already been paid, if you can sell the design and get some royalty payments, why wouldn't you turn those old plans into cash?

And of course there is a huge industry of Chinese clones and other suppliers that will provide replacement parts that are not genuine.

Be prepared to pay, though :)

It’s still possible to order new and original parts for SAAB models, almost 20 years after they went under. The spare parts are made by a separate company which is still going.

IIRC, by law manufacturers are required to maintain parts and service for vehicles for a minimum of 10 years. Whether superseded, discontinued, whatever.

It depends. Lots of parts are shared by multiple models or even companies so it may be the case that nobody has made for example a new water pump specifically for your car for 10 years, but the design is the same as the 2025 something else so you can just use that one. There are also warehouses with older parts that can last for years. You can also pull replacements from junked cars that have not been crushed yet. In some cases third parties manufacture replacement parts when the supply runs out, but those replacements are often of poor quality and sometimes are only vaguely shaped correctly and require extra work to actually fit on your vehicle. Keeping old cars running is a challenge, especially if the car was obscure when it was new.

Yes. Auto manufacturers tend to have contracts with different tiered automotive suppliers that have heavy-hitting production lines for current vehicles, and also maintain a 'service' department where these style of products are produced. The tools for producing these parts have really good lifetimes, and you can take the tooling and put it into whatever mold machine you have written the program for, or set it up for another machine.

In my experience service departments are basically a large warehouse with a small set of assembly machines running at any given time where you are setting up time to produce some random part for a day or two and then change to something else, whereas the real production assembly lines are designed to produce as many of X part for the latest car as possible.

Several of the old mold machines where I worked that made parts for this service business ran DOS, with PCMCIA cards to load programs. I helped a process engineer get these PCMCIA cards working on his contraband laptop running win98 (obviously banned from the network) because we could never get them working with anything newer. This was in like 2021.

A lot of parts are refurbished too. Transmissions, differentials for example.

Their subcontractors do.

For traditional vehicles, there's typically a large marketplace of first-party and third-party auto parts for vehicles going back several years. Depends on the make and model, but usually yes.

That said, Tesla is a very unusual automaker in most senses and I'm not sure what their aftermarket parts situation is.