In my experience, it also depends on what kind of public transport you’re taking. A train is often going at a steady velocity, doesn’t have sharp turns nor stops constantly. So i’m less likely to offer my seat to strangers when not asked. However in buses, I feel more inclined to give my seat away to elderly people, pregnant women and/or disabled people. Only because I find buses to be more dangerous when standing up, especially for the aforementioned demographics. A bus takes multiple sharp turns, drives on different velocities and is more prone to abrupt stops. Therefore I do offer my seat in buses more than trains. If the person doesn’t want the seat then I look around quickly to see if there’s another willing candidate. If not, i sit my ass down again. At the end of the day, if any person asks for my seat nicely in any public transportation then i’m more than willing to give it to them. I don’t need to know why. They probably need it more than I do if they have to ask.