Because the census is utterly clueless on how to properly classify people. The Canadian system is far superior.
How's the Canadian system?
It's not perfect either, but:
The census (actually, the "National Household Survey" [NHS] which is an optional form that 1/3 of Canadians get along with the mandatory census) asks whether or not you're a visible minority. If you're not a visible minority you're either White or Aboriginal. (because I guess calling the original inhabitants of this country minorities is offensive?)
Because Canada does its worst to make them invisible.
(Or because that's dealt with in a separate question.)
South Asians used to be classified as White by the Census guidelines once. The reason they aren't anymore is that so many of them checked the wrong boxes. Quite a few Middle Easterners also do.
