I think you are confusing Amtrak with Greyhound. When I’ve ridden Amtrak, passenger base is the same as on a legacy airline, especially on the Acela corridor. As far as subways/metros are concerned - the folks I have seen riding the metros in Paris, Amsterdam, and London are as diverse as those I see when I ride the PATH and MTA in my part of the world.
I have ridden eastern corridor Boston to Orlando. Very diverse. Lots of crime. Stopped frequently to give criminal to police.