I think I missed this before, and I feel the need to reply: Because G1 Astrotrain, is modeled after Japan's most-famous locomotive. He's THE steam locomotive that is known and associated with Japan, and defines what "Japanese locos" look like. A non-Japanese alt-mode for Astrotrain's train-mode, would be kind of like making Tracks a Ferrari and Sunstreaker a Mustang. While their alt-modes do get updated, they generally keep the same "look and feel of the original alt-mode's country of origin", as each country tends to have their own spin on how things look. While most people can't tell US from German from Japanese locos, they all do have their distinct looks. And Astrotrain is "ridiculously, stereotypically Japanese" as locos go. So any new version of him, should probably be Japanese.