It all comes down to SECURITY.
This subject gets done to death about four times a year!
The answer is simple, when you can 100% guarantee that the system is totally safe from terrorists who might physically take over a remote ground control station, or hack into the system with more powerful transmitters, then you may get your pilotless airliner, always assuming you can get someone to fund the R & D and you can find insurance underwriters who are prepared to insure such aircraft, passengers and third party liabilities.
Similarly with driverless cars, can you get them insured? Also, don't forget every single road sign and traffic light will have to have it's own transmitter as optical recognition won't work when the driverless vehicle is stuck behind a truck!