As sawdust are in fact small particles or pieces of wood which can be easily carried around by wind, it may be a fire hazard as wood can catch fire quite easily especially in an industrial environment where there may be engineering or welding works going on.
While these may be some reasons why there may be restrictions for the woodworking industry, there are still some factory units that can allow carpentry works. However, it may not be that easy to find factory units which allow carpentry works due to the nature of works & operations.