Very location dependent. I grew up in some semi-rural areas and everyone says hello to each other in passing, and you can tell by their body language or reply whether they're up for a chat about bollocks or not.
Urban areas at rush hour - particularly London - is a different ball game. A thousand, maybe 1500 people (I don't know what the capacity is these days) people crammed onto a line of trains, and not a single word being spoken between anyone. I have never felt a feeling of being somewhere heavy populated but being so utterly disconnected since.
Yeah I get it - there's folk who don't want to talk (fair enough) or can't be fucked with pre-work or post-work talk (even more fair enough), but nothing so much as even an "alright mate". I suppose public transport attracts it's fair share of... unstable people, so maybe it's just easier and safer to zone out.
When two people come together in a "chat shit" mood though, it's really interesting who you can end up speaking to.
¯_(ツ)_/¯