An older, 70s or earlier, Olmo bike I have. 56cm seatube, and 54cm toptube with an adjustable stem that goes up or down 9cm, and only adds 6cm forward reach to the bars.

A 56cm seattube trek1000 has 56cm toptube +12cm of stem. That's effectively 8cm longer than it used to be. I have some 80s bikes that are in between these 2 measurements. In fact, I'm very happy with the fit of an 80s 50cm seattube, 55cm toptube bike (I guess 8cm stem).

Why have bikes stretched out over the years? Is there an advantage to a longer reach beyond knee clearance?