Ubisoft sold keys ad different prices. Some of the "cheap" keys were activated in "expensive" areas. Rather than identifying the resellers and shutting them down (though they may have done nothing wrong), Ubisoft identified the keys, and revoked them.
Note, Ubisoft made a profit selling these keys to authorized distributors, and the users paid for a (at the time) valid key. But Ubisoft thinks they could have extracted greater profit with a different sales plan, so they revoked them all to try again. Too many "save, restart" games played by Ubisoft.
I hope they didn't try this stunt on Australian customers. We have "parallel importation" legislation forbidding retailers from trying to prevent people monopolizing sales channels againt people who import cheaper from overseas. Back in the day, the ACCC actually forced retailers to stop supplying DVD players that where not multiregion, although the bloody conservatives put a stop to THOSE shenanigans. Hell back then the ACCC even sued Sony for going after mod-chippers.