The slacker seat tube angle does not position the saddle further from the stem.

The saddle actually will move closer to the stem, since each rider will arrive at their preferred balance point above the pedals by sliding the saddle fore and aft, and as the seat tube angle moves "rearward" from the bb, the rider compensates this by sliding the saddle forward.

Remember, that as the seat tube angle goes "slack" or rearward, the bike's head tube gets pulled back with it, making for an effectively smaller (shorter) frame and wheelbase.
Only if the top tube were also made longer could the bike's fit and wheelbase not shrink, but bikes with a slack seattube angle don't usually have any longer of a toptube than on steeper bikes.

This bike has very slack angles, 71-degrees, and a 59cm top tube commensurate with it's 61cm frame size.

Notice how the Steyr's resulting setup loses 2-3cm of effective length as the seat cluster has moved so far rearward of the nose of the saddle.
The saddle is in the normal position relative to the bb, but the 59cm toptube has been pulled rearward, shortening the "reach" and wheelbase, thus shortening the rider's reach to the bars.
The resulting bike actually fits me just about like a smaller 57cm bike that has steeper road geometry (say with 57cm toptube and 74-degree seattube angle), and the post-1978 Peugeot U09 doesn't even need as long of a stem as the Steyr Clubman.