Do all models on grabcad have no textures?
Any model, I downloaded, have no textures. I guess CAD models don't support textures at all, right?
If you export a model in some universal format, such as STEP, STL, etc., it will most likely not have texture, for compatibility purpose.
If you open files on a specific software that allow textures, there might be textures available, if the author have set it up properly. An example is this CAD model of Raspberry Pi 3 Model B Reference Design Solidworks CAD Raspberry-Pi Raspberrypi Rpi, which have textures if opened in Solidworls Format. Opened on STEP, STL or Parasolid, there is no texture.