There's not really an answer in the article besides not wanting to clearly identify a point in time, and wanting the cars to match in some sense the personalities of the characters that drive them.

The show's aesthetic takes a high dose of "cassette tape futurism", juxtaposing advanced tech with the primitive. Also featured are anachronistic computer terminals, VHS tapes, and music records. The car choices play well with that.

N.B.: Particularly primitive is Lumon's surveillance of severed employees. This hardly makes sense when the chips can be activated remotely, but heavy surveillance would kill the exploratory velocity of the story so that was a good choice, in my opinion.