In the Northeast, it's often cheaper, and pretty much always faster, to fly than to take Amtrak, unfortunately. My family tried to get me on a last minute family gathering over the holidays, for example, and Amtrak was going to be over $400 round trip, and a round trip flight was less than $200, and about 2h30 quicker each way. If I look up the same trip saying I want to go from NYC to Boston today and return Tuesday, taking Amtrak at crazy early or late hours would let me have an 8+ hour round-trip come out to $285. Round trip flights would run $427 pretty much any time of day and take 3 hours in total. For me, as a younger guy often travelling solo, it might make sense to just wake up stupid late and be on a 2am Amtrak train to save some money. For people with kids, elderly folks, or anyone who has time commitments that mean they can't do that, the $427 flight at 10am sounds a lot more appealing.

It only gets worse as the distance goes up. NYC to Montreal is only a $153 round trip on Amtrak if you book in advance to snag one of the cheap seats, but it takes 11h41m each way. Round trip flights going direct run $242, but going and coming take only a quarter of the time for going one-way on Amtrak.

Oddly enough, going south, Amtrak actually makes sense. Booked far enough in advance, I can go from NYC to Philadelphia, Baltimore, or Washington, DC. for between $30-$50ish, last time I looked. Flights are more expensive and only save me about 90 minutes on the longer legs. I have heard that outside of the NE Corridor, Amtrak is much more affordable, but I don't know how true that is.