Such armor could be torn off by a mob of zombies, and it would severely slow down the suit-wearer. In addition, you'll note that the joints are not actually covered by metal in all places. It's the chainmale (underneath the armor) that would provide the most protection from zombie bites.
Regardless, there are plenty of modern light-weight protective suits that would be more useful in a zombie apocalypse. Plus, a lot of those suits of armor need to be fitted specifically for the individual and require a lot of maintenance.
Some good background: