Originally Posted by Doug Fattic

Before mountain bikes, aluminum seat posts were only made fairly short to fit frames with level top tubes. Nobody wanted any more length (and weight) than necessary. I built some custom frames for really tall riders in the 70's and early 80's and the seat tubes had to be really long (making a big frame) so the seat post could be inserted far enough to get below the limit line.

In the same way in that era, most aluminum stems couldn't be raised very high because they were designed to have a minimum amount inserted into the steerer (to save weight) . They were designed for a racer's position.