Cumin in Taco Seasoning?
I'm going to supplement Cindy's answer,  by addressing this part of the question:


  When and why did cumin get associated with tacos? 


According to Wikipedia, Serious Eats, and History.com, the cumin was brought by workers the Spanish imported to Texas from the Canary Islands in the 1500s, who themselves were the descendants of North Africans and hence had a love for cumin.  These workers introduced cumin into Tex-Mex cuisine, particularly Chile Con Carne, and when Willie Gebhardt created the first bottled "chili seasoning", it included cumin.  Many Americans encountered Gebhardt's seasoning a generation before they experienced any other kind of Mexican food, forever associating it with the cuisine.  And, for that matter, used Gebhardt's for taco meat, as my Oklahoma branch of the family did back into the 1930's.

The reason you don't encounter it in some Mexican restaurants it that the culinary staff are from Mexico, and not Texas or near Texas.  As such, they never "picked up" cumin.

(and yes, this does mean that Thrillist is wrong about the origin.  India was not involved)