this is funny because chit chat is generally very welcomed on the nyc subway (and practically everywhere else), especially on the weekends when you can talk to tourists and give directions and have nice exchanges. Obviously rush hour isn't a great time to chat but otherwise tons of people just love to talk about anything, anytime. It's highly contrasted to how very very reserved everyone is in Atlanta (my current home) and almost every other US city outside of new york.
I have lived in NYC for more than three years and feel like I've probably only seen a conversation between strangers maybe 5-15 times ever? I take the L and NQRW the most, perhaps this is a hyper-local phenomenon with your line?
I do see the 'tourist asks if they can get to ___ on this train' conversation but don't really consider that in the context of the OP.
It's up to you to make a pithy observation + smile or comment on the weather or give up your seat + say hello. Make the subway you want! I rode the A/C & 1/2/3 mostly, fwiw. West side manhattan is just friendlier I guess ;)
