There are many ways to look at this. On one hand, you could say that people are selfish louts who seldom look up from their phone screens. Chivalry is not only dead, it's frowned upon.
But the fact is, people are reluctant to give up seats not only because they enjoy sitting in them, but also because they're unsure of the etiquette. Will a "woman of a certain age" be offended if said seat is offered? Will she take it as insult or generosity? So there's the ambiguity issue.
But beyond that, there is, I was thinking yesterday, the acceptance issue. I often refuse the few seats offered to me. "I've been sitting all day," I say. Or, "I don't have many stops to go ..." (in actuality, I get off at the end of the line).
Yesterday, however, I gratefully accepted the seat. I'd been sitting all day, so I didn't need it. But I was glad to mute the Metro experience by sticking my nose in a book. I accepted the seat the young man (and he was a young man, with a neat haircut and wireless ear buds) generously offered. And I accepted it without hesitation. Graceful acceptance: sometimes it's pressed upon us.
(Grabbing a seat no problem in this empty train!)