[beaner]

Because laypeople don't think of those things. The divide in the way people look, the environment of their countries, how they sound, and what they believe, is split in Asia by the Himalayas. Obviously there are many differences between the countries but it's easy to see why conceptually some might group some of them together into 2 large regions. Also Indians in America don't generally refer to themselves as Asians when speaking, so if their goal is to be perceived as Asian, they are not helping themselves.