i believe this dates back to jarateking's clean tf2 .vpk file pack days where surfaceproperties.txt would remove decals from the walls(i think) and also dandruff and smoke when shooting surfaces such as floors with hitscan(really nasty frame drops on bad pcs from those particles btw)
and i dont remember now but i believe the original file provided by jarateking used the metal footsteps which were fine at the time because people didnt yet fuck around with spy decloak sounds en masse
its just that it was shipped with m0rehud for reasons beyond me