At some point people just quit and go work for McDonalds. Unless you literally force them at gunpoint to work the rails, you eventually have no rail workers.
So far the working conditions haven't got that bad for enough to be noticeable, but at some point you'll have no new employees and the old ones will quit or die off.
This is also why Republicans fight so hard against safety nets, nationalized healthcare, unions, worker rights, etc. The more desperate and struggling people there are, the more workers for these horrific, anti-work life balance jobs there are. The Fed purposely pushes for an economy with a set minimum of jobless people, purposely encouraging desperate out of work people who will take anything to put food on their plate.
I also think Democrats are happy to let them be the bad guys, while they make a lot of noise and token efforts to make things better, but never enough to hurt profits.
So far the working conditions haven't got that bad for enough to be noticeable, but at some point you'll have no new employees and the old ones will quit or die off.