this was my question as well, like other people have pointed out OBD2 can get you diagnostic information but cannot actually control movement of vehicle or other parts on the car
On my car (Mk6 VW) there are multiple CAN buses which are separated by a gateway device. A device plugged into the OBD port has to negotiate with the gateway in order to access the other buses, but once it has done so can control the windows, lighting, instrument cluster, etc.