Attack vector
Your suggestion with an autoland feature is a very good attack target for anybody intending to down a plane.
Crack the system, and you won. No-one will be able to stop it from happening, by design. And it even can possibly be done anonymously, from remote!
You think, autoland will stop a harmful end? No, just irritate the computer by erroneous sensor input, or even data that will cause the autopilot to crash the plane.
Adding more complexity adds more attack surfaces.
If you look at the reports about the 'safety' of the data buses in planes, it is a miracle to me nothing happened yet in that direction. Up to now, an attacker must still be physically on the plane. Offer external system overrides and it will be mis-used sooner or later.