I have several old cars, and plastic interior parts are difficult to find if molded in a specific color to match the interior color. Newer cars tend to have molded pieces in only two or three colors.
My '68 and '77 Eldorados will never have the collectability of a GM intermediate from the 1960s or early 1970s, so I don't expect reproduction parts to be made. I'm somewhat surprised that parts aren't available for Steven's '69 GP. That car was very popular when new.
I also have my late parents' Rivieras. The '89 has an electronic dashboard (CRT screen). The newer one has a more conventional dashboard, but both cars might as well be junked when the electronics fail.
Eventually, there always seems to be some demand for cars of all eras. Whether it's because a person's relative had one, or a neighbor or family friend, someone will want something that most wouldn't want if given to them. With all of the electronics, armrests molded in to the door panels, parts meant to snap into place one time and damaged when any attempt is made to remove them, and engine compartments impossible to work on for the average person, most people won't want to bother preserving or restoring the majority of newer cars.