They either don't know the physics underlying proper TE shaping, know but don't care enough to do anything about it during manufacturing, or disagree that it's actually a better way to shape a foil.
My guess for most foils is that they just don't hand-finish them to a degree where anyone is going to take the time to address this. When you pull a carbon foil out of the mold, it's faster and cheaper to just snip the outflow off, sand it to a commercial grade finish, then send it out the door. Only the top of the line hand-made race foils like DeltaHydrofoil ever get enough TLC to be shipped with a hand-finished surface. I remember back when the Banga race foils were brand new, I emailed the manufacturer who assured me each foil underwent hours and hours of post-manufacturing hand-sanding for this exact reason.