Its not like that at all. Planes are mostly fly by wire anyway today, so i m not sure why it would be harder to do that. You 're aware that drones fly remotely , right?
All the technology exists for me to build a drone swarm to patrol my house constantly on the inside and out, deliver me a video stream, and to deter intruders with non-lethal force. That doesn't mean I just need to order the parts, assemble them, and use.
There is no off the shelf remote fly-by-wire for an Airbus A320 or any other passenger jet. Plenty of companies have done it as a one-off thing. This is for either testing UAV systems or using the plane as a crash test vehicle. This usually involves the same team of engineers that equipped the aircraft monitoring every single parameter in real time. The military has actually received criticism for conducting weapon systems 'tests' in this manner.
There is a huge difference between that and commercial operations of such a system. In a commercial environment, you can't have a team of engineers on constant standby. For planes flying for research purposes over unoccupied areas a high risk of total loss of control is completely acceptable. Commercial and military remote control aircraft all have systems that intentionally crash the vehicle if communications is lost and it leaves a designated area. This prevents potential loss of life due to mundane software bugs. You can't ethically build a system that intentionally crashes an airliner full of people as a response to a software bug.
As to "why is it not implemented" - because it would create far, far more problems than it would solve, without a measurable benefit.