Older vehicles 5-20 years old are easier to get parts for. Body and repair shops are waiting months for new car parts (especially driver assist) whereas old stuff is readily available.
That's true for used body parts and drivetrain components but not for accessories and electrical components, especially computer components.
As for used parts, keep in mind that this article is about insurance companies totaling cars, not owners willingly taking them off the road due to parts availabilty. Many insurance companies will not authorize used parts for repairs as they don't want the liability if they fail and contribute to or worsen and injurious crash.
Since 12.6 years of age is the average, parts for cars from brands such as Saab (d. 2016), Scion (d. 2016), Pontiac (d. 2010), Mercury (d. 2010), and Saturn (d. 2009) become not only harder to find, but an insurance company that authorizes used parts for replacement has no recourse to go after a manufacturer that's no longer in business in the event that replacement part is at fault.