All* forks are spaced the same, and there is no special considerations needed for front wheels. So more front wheels exist in the world for fixed gear riders to use. Its hard to impossible to convert road rears into being able to be used for a fixed gear. Wheel manufacturers only make carbon wheels for racing, track racers basically only use rear disks. So there is not really a market for fixed ready rear trispokes, etc.


*In bike terms all means 90%.