I always figured it had more to do with the kind of systems were using back in the days of old - flat and dull sounding by default. Most cars I remember being in, in the 80's and 90's maybe had quad 4" speakers with no tweeters, and a portable radio or walkman was pretty lo-fi sounding as well. So the bass and the highs would be hyped up to make it sound better for the average listener?