80's are gone dude.. you asked why and then listed cars from 30 years ago..
I have no idea why manuals aren't as popular as they once were, but I get the feeling people now simply tend to not know how and or lack the desire to drive a stick. Conveniance is on the side of an automatic car. Look at what is happening , People own cars for fewer years now, switch on to something different. Stick cars may seem like to much of a hassle for short or city driving..they need clutch eventually. Its the same mentality with the driving experiance as well quickest to and from a to b.