I think the notion of a “BIPOC coalition” has many angles. Many black political thinkers and academics focus on a black/white binary, and extending the concept of “black” to “people of color” was natural. This was also appealing to white democrats, whose coalition with black people is heavily focused on fighting purported racism and discrimination in return for loyal democratic voting.
Couple that with the prospect of America becoming a majority non-white, it’s easy to see why the broader left of center embraced the rhetoric and policies they did over the last decade—e.g. reframing policy issues like immigration and policing in racial justice terms.
The problem is that “white racism” as a lens for understanding America—widely shared by modern liberals—is a poor tool for understanding Latinos and Asians.