Planes can (and do) follow a set of waypoints. And have been capable of doing that since the introduction of Inertial Navigation Systems and today they use GPS backed up by INS. Nowadays, theoretically planes COULD be built that do the entire flight autonomously if everything keeps working. Currently you need a human in the cockpit to handle comms, switch settings, press buttons, and handle anything out of the ordinary. The systems we have to do unmanned flight are not as reliable as having a well trained human in the mix, so nobody wants to use them. And it's very likely it'll stay that way for quite some time. On top of that those systems only work if everything keeps working as expected. Throw a failure into the mix (even something innocuous) and things will go bad fast. No matter how slim the chances, I'd like a plane I'm on to be flow by something that can handle something unexpected. Be it something small (like an engine exhaust running hot and diverting to an alternate before something goes bad) or something large (like the Gimli Glider or the Sioux City DC-10 crashlanding). It's not a guarantee for success, but it gives a chance.