It might have something to do with the fact that most state laws require bikes to be sold with pedal reflectors. I haven't seen a clipless pedal with reflectors.

Here's a typical example from Michigan:

MCL 257.662
(4) A person shall not sell, offer for sale, or deliver for sale in this state a bicycle or a pedal for use on a bicycle, either of which was manufactured after January 1, 1976, unless it is equipped with a type of reflex reflector located on the front and rear surfaces of the pedal. The reflector elements may be either integral with the construction of the pedal or mechanically attached, but shall be sufficiently recessed from the edge of the pedal, or of the reflector housing, to prevent contact of the reflector element with a flat surface placed in contact with the edge of the pedal. The pedal reflectors shall be visible from the front and rear of the bicycle during the nighttime from a distance of 200 feet when directly exposed to the lower beam head lamps of a motor vehicle.


Actually, now that I read it, I wonder how they sell clipless pedals at all in Michigan.