The sheer amount of cosmic radiation would drown out any WiFi signal, it would even drown out a wired network connection at normal voltages, spacecraft usually use 50 V or higher on inter-machine communications. Shielding has to be ridiculously thick in order to get packet loss down below 50% as it is. Ethernet is just not suited for space applications. And even without those issues, the signal would be fighting with the array of communications antennas the station needs.
Then there is the cost of running the cable: bulkhead couplers that can withstand the pressure differential between the interior and exterior of the station as well as standing up to the extreme temperature on the exterior would be very cost-prohibitive (Especially on something that only has about 5 years of life left). Not to mention the risk of cutting holes into the doors, even if they had available space to make the holes.
But the most important reason to put stuff like this on the outside is that there isn't much space on the inside to add anything. Imagine lining the walls, deck, and ceiling of a 737 with server racks, and that give you a good idea of what its like on the station.
But all that aside, there is no point to such a high-speed network. Other than the Command and Control data, voice/video communications, and personal internet traffic; the bulk of the data produced on the ISS is with experiments, and their data is stored internally and sneaker-netted back to earth with the experiment's modules (not too dissimilar to a rack-mount server). Either that or the data is gathered on the experimental subjects after they've been returned to earth.