Firstly the GPS satellites send only pseudo random codes consist of ephemeris and almanac. It contains current location of satellites and timing signal. It does not request for location of any receiver on earth. It's just one way communication. How will merely reflecting a signal add latitude, longitude and currency serial number without any electronic circuitry processing the signal. It's true that with VLSI technology, such circuit can be miniaturized. However, for circuit to function it will need power, either small cells(which will eventually runs out of energy, so will need everyday charging) or through solar power. Please note that power can not be wirelessly transferred like information and power stored in a cell is proportional to its size unlike electronic circuitry.
Please use common sense that there are millions of GPS users and if satellites were to receive signals from each of these users, then it would need a huge server and processor to process their locations. The server would further require cooler facility to avoid overheating and so on.
FYI, the receiver processes the signal from the GPS satellites and computes it's position based on the recieved signal UpTo certain accuracy and GPS signals can only be used for surface positioning, not underground or subsea positioning.
