Because that is a regular thing.
Regular but how? I've not been to the US but it is pretty obvious that many Indians live and work in the US, not just Indians, Chinese as well. That's something that is true, which is a common sight, i.e if you go out on the streets on a regular day in almost any state of the US where most Hollywood movies are shot you will see Indians and Chinese.
I believe there is nothing like a marketing strategy, if yes, then that's a pretty lame one and I believe big movies don't require that, like Deadpool, that one role of an Indian Taxi Driver was not a big deal, it was a small role but managed to get a lot of attention, that's just the magic the movie makers put in the character nothing because of the nationality. The true fact is that many Taxi drivers in the US are Indians so why wouldn't it be great to cast an Indian to do that role?
They're presenting the truth, there are Indians and Chinese in the US, so if they do not present it the same way in their movies that'd be going south of what's the reality.
Though if someone is doing a Hollywood movie that is set in the ancient period (assuming the movie is centered around Romans or the English, etc.), I do not think there would be much Indians or Chinese in that movie.