Items sold on AliExpress are often posted on OzBargain. These are the rules for AliExpress postings on OzBargain.
Most overseas users are representatives of companies. By banning all overseas users, this prevents undeclared reps (and 1 post wonders) from posting AliExpress deals.
An AliExpress listing with very low quantity is not a bargain because it has very limited usefulness to OzBargain members.