Certainly, able-bodied people are basically expected to readily give up their seats to their incapacitated fellow citizens. As people's eyes are mostly glued to their phone displays these days (as seen in this chapter), they may not always notice another needy person standing in the aisle, or they might use it as a sort of excuse to not take notice.
I can't really speak with authority on how this stuff would ultimately shake out in Japan, but in Korea elderly people are anything but shy and will make themselves noticed in some way. Also, some of the seats are explicitly reserved for only pregnant women, basically as a way to make pregnancies a little less scary in a country with precariously low birth rates, but elderly people mostly seem to think they own the place, and sit there, too. Pregnant women receive a sort of pendant they can wear to indicate their eligibility. Normal people where the God-complex-after-the-age-of-sixty gene hasn't triggered yet will rather stand than occupy a seat like this, even if there's no one around at the moment who'd be entitled to take advantage of it.
