As far as I can tell, it is because the system only allows a limited number of locations to be specified .
I know that, while I can promote Australian shipping, New Zealand buyers have to contact me. No problem with EuroZone, but former Soviet Union must contact too.
Are you using Calculated Shipping?
And I doubt metric is the problem. The eBay system does a rough calculation (since they are an American company) when we use Imperial measurements, but most of the world , and Canada Post, use metric as the default.