The prob isn’t the fake slide as much as intentionally sliding late for yards and to draw a penalty. Hitting the slider is so over penalized that the only way to avoid it is to wait down the field with no forward momentum at any given moment so that the slider can initiate the slide and hit you headfirst. It’s an insane policy that leads to more injuries because it incentivizes sliding late to draw the penalty after the defender has committed to the tackle.