How come no one ever mentions instruction curriculum in these discussions?

An independent instructor might "solo" a quick learner, then jump right
back into the airplane for many more hours of dual.

A structured 141 school's program might require the student to
demonstrate proficiency on more maneuvers, be comfortable on the radio,
cover more emergency procedures, take a pre-solo stage check ride, etc...

My 141 school required me to experience demonstrated stuff like
accelerated stalls, secondary stalls, and to perform pattern trips and
very low approaches with simulated aileron, elevator, and rudder
failures, as well as some instrument failures. I also had to do a
pre-solo stage check with a different instructor.

I very successfully took my FAA check ride well before the national
average hours (including three stage checks for ~ 5 flight hours), yet
my symbolic "first solo" was farther along than many who brag about how
quickly they were able to do so.