I think he has made a selection, the dates below the pictures suggest this, also the consistently dead expressions. My initial thought was that the photographer must be a scary-looking guy, but if the subjects of the photos were caught unawares then that would not apply.

Most mass transit systems are handling a bunch of people who are simply getting through a dull and routine part of their day, they just want it done with so that "real" life can proceed. The passengers are in an unnatural space, usually confined more closely than is comfortable with a random selection of strangers, any of whom might well be a threat, they are frequently tired and/or stressed and [at least in the UK] they are probably being overcharged for the privilege.

No wonder they don't look their best.

Getting out of commuting was one of my best-ever decisions.