That you do not understand it and find it "baffling" does not make it so.
The reality is these people do need to fly. Being pro environment is irrelevant to the problem. When my boss says "they need you in Texas, get on an airplane", I don't say "but boss, what will Greta say?", I get on the plane and keep my job. I'm also not burning 2-3 days of my vacation in each direction to get to Florida.
I took trains in the US. From Indianapolis to Chicago, the train was 2 hours late. It arrived 2 hours late, and took an hour more than a car. This is a trip of just over 150 miles.
For me to go on vacation, it is 1000 miles to Tampa, Florida. This is a 2.5 hour flight. If I include the airport inconvenience, and the benefit of not having my junk touched for national security, I'd happily spend twice that in total travel time. If you have a train that can do 988 miles in 5 hours, on time, and less than a flight, I'll take it.
We fought a world war because the Italian President and later dictator ran on "making the trains run on time".
Even if trains didn't suck, and tomorrow they were all on time and all amazing and never had strikes that ruin vacations, it would still take 20-30 years for Americans to trust their job or their vacation to a train.