If an airline did anything wrong to a customer, the customer can complain to the DOT, and the airline has to answer to the DOT, and the DOT keeps track of complaint statistics, so the airlines has an incentive to fix things.

If Amtrak screws a customer, you're at the mercy of Customer Relations because Amtrak only answers to Congress, and if your congresspeople won't advocate on your behalf (which mine won't, and most others won't either) when it comes to Amtrak issues, then you're SOL. Amtrak can go and break every consumer protection law out there, and get away with it, if Congress doesn't press the issue.