I'm guessing it's a combo of a) aircraft utilization/capacity and b) 5th-freedom passengers. Mostly (b), i'd imagine there is a lot of traffic on the trans-atlantic leg, plus of course they can "pick up" passengers in Europe.
I suspect the sheer number of Indian passengers and "5th freedom" passengers on these routes explain why AI has never added transpac service from the US to India. I don't think they'd pick up as much "Indian" traffic in TPE, NRT, HKG as places like LHR and CDG