"Holy cow that's awesome! I'd never be able to do that."
"look how close he is to the ground - that's dangerous!"
Modern skis that can actually carve.
The marketing concept that you need a freestyle board even if 90% of your time is spent outside the park/pipe.
Misconceptions (uncomfortable, cold, difficult, only good for carving/racing) or stigma (uncool, skier-like) of hardboots.
"I carve fine on my softboots." (no, you don't)
"I don't want to be a beginner again"
Not enough days spent on the hill to justify a second setup.
Lack of mainstream exposure - the "is that a snowboard?" questions didn't start until Alpine was dropped from the Burton catalog.
Fear of change, complacency, acceptance/obliviousness of mediocrity.
The idea that the most important skills in snowboarding happen with the board off the ground.
People like being able to walk around in softboots - they would rather have comfort while walking than performance while riding.
Plain stupidity.
(mind you, I don't really have a problem with the size of our population. I'd just like to sustain it.)