That's because Hasbro and Takara have a contract between them which forbids them from "cross contaminating" each other's markets. Tomy can sell Thomas the Tank Engine toys here, because Hasbro doesn't own the rights to that here. They can sell Transformers in each other's markets in special cases where they have obtained permission from the other party.
e.g. toys like MP02 Ultra Magnus, MP04 Convoy Perfect Model, MP Ghost Starscream, DotM Jetwing Optimus Prime etc. are all Takara(TOMY) toys that Hasbro was able to distribute for sale here in Australian stores because they had special permission from Takara(TOMY). But normally Hasbro and TakTOM don't sell their Transformers in each other's markets.