The Aircraft is perfectly capable to perform an Autoland with the L HYD System failed.
It's just a liability/certification issue.
From the B777 AFM
Demonstrated compliance with the AFDS airworthiness performance and integrity standards does not constitute approval to conduct operations in low weather minima conditions.
Automatic Landing With One Engine Inoperative The autopilot system has been demonstrated to perform satisfactory automatic landings with one engine inoperative at the beginning of the approach. The demonstrated configuration was:
LAND 3 OR LAND 2 annunciated Flaps 20 or Flaps 30
The automatic landing system has been demonstrated to perform satisfactorily with one engine inoperative in the following wind conditions:
Headwind: 33 knots Tailwind: 20 knots Crosswind: 29 knots
The performance was demonstrated with and without autothrottle on the operative engine, and with and without Thrust Asymmetry Compensation.
The automatic landing system has been demonstrated to perform satisfactorily following an engine failure during approach.
Automatic Landing With A Single Hydraulic Failure The automatic landing system has been demonstrated to perform satisfactorily with a single hydraulic failure to either the left, center or right system.
Verification Altitude For Autoland
On approach for autoland, verify LAND 2 or LAND 3 status, as appropriate, at 500 feet AGL.
Normal Procedures 777 Airplane Flight Manual .
Section Autopilot Flight Director System, continued from previous page A121788