It’s simply a by product of increasing reach and needing to maintain a reasonable seat to handlebar distance. A side effect is shifting body weight forward which helps keep the front wheel down when climbing.This has been inflated as meaning ‘better climbing’ like suddenly it creates 50watts more power.
loads of bikes are too slack (plus coming with a layback post) to actually allow you to setup in the correct position for pedaling efficiency
Funny how roadbikes (where pedaling efficiency seems to be quite important) have seat angles of 72/73degrees and mostly use setback seatposts (TT/Tri bikes are a different matter as its more linked to aerodynamics/utilizing a different muscle group).
Although I’m not a KOPS subscriber (it’s more happenstance than scientific fact) it does seem widely accepted as a starting point for good pedaling dynamics.