There is one aspect where flying beats trains: checking luggage. If you have big suitcases it's a PITA to get them on and off the train. And changing trains means taking the bags with you, unlike flights where bags are (usually) transferred.
Even when you do have to pay in the US it is typically very generous. Larger size and weight allowance, and you won’t get dinged for being even a few kilos over. And the bottom tier of frequent flyer programs (which is usually trivial to get and keep) waives all these fees anyway. I can’t remember the last time I paid for luggage allowance outside of a trip to or through Europe.
(It's a song called United Breaks Guitars that you may remember from over a decade ago).
You were the local shopping stimulus all along.