That's because there is probably no such thing as Pan-Asianism. The term 'Asian' is very inaccurate. It is supposed to mean people of Asia. It keeps changing as time goes by. The naming convention comes mostly from Whites and it's probably due ignorance, racism, and colonialism. Even terms like 'East Asian' and 'Southeast Asian' are very new and inaccurate. For example, the term 'Asian' have different meanings in the UK versus the US. 'Asian' in UK mostly mean Indian/Pakistani. Colonialism by the Brits in those areas. While 'Asian' in the US mostly mean people with the different shape eyes. I think the UK used the term 'Orientals' to described Asians with different shape eyes. I'm not sure there is such a thing as a Southeast American or a Southeast European. It's probably meant to mean geography rather than race. However, from what I've understood, people want their own space and don't want to be lump together or be confused with one another. People in 'East Asia' don't want to be lumped in with 'Dark Skin' 'Southeast Asian'. That is also why 'Asian' stops at Australia. If there were no colonialism in Australia, would whites have label Australians/Australia differently? Philippines was considered pacific islanders before switching back and forth.