The maintenance burden is huge. Every time any part of the autopilot / land system fails that requires a rectification / box-swap the groundcrew have to carry out a full autopilot functional check with full autoland. That's about 8 hours work...
This of course includes the ILS and RADALT systems.
Not to mention keeping a log of all the boxes status after every flight, so that any spurious fault trends can be monitorerd.
I seriously doubt they have the manpower for that...