Reddit mentions of A Part, Yet Apart: South Asians in Asian America (Asian American History & Cultu)

This definitely has a lot to do with which communities were in the U.S. in the largest numbers. “Asiatic” historically referred primarily to Japanese and Chinese, though even the Asiatic Exclusion League understood that “Asiatic” included “Hindoos."

That said, it's complicated. While the 1923 Bhagat Singh case made clear that Indians weren't legally considered White, I believe Indians were categorized as White in the 1950-1970 census, and Indian (and other South Asian) Americans had to fight for inclusion in the "Asian" census category.

For folks who are interested in the topic, I totally recommend a book called "A Part, Yet Apart: South Asians in Asian America" edited by Lavina Shankar (https://www.amazon.com/Part-Yet-Apart-America-American/dp/156639578X).