When I was in the UK, I took the Virgin Rail from London to Manchester. The additional room and ability to walk around made it so much better than a flight. I would have paid more. The time difference was negligible once you count all the extra screening time for airports.
Airlines are better, not just because planes are faster, but because of flexibility. You can find a space somewhere and build a new airport, or add a new runway to an existing airport and use less than one thousandth the land the rail line will require. The planes you fly to one destination can suddenly be switched to fly to almost any another destination, in a day.
Yea, the comfort of trains is better, but thats about it.
Nevertheless, we don't have the same security circus when boarding train.
Looking at what is happening in California, cost is the largest issue[1]. The other reason is the US optimized its rail for cargo which it does well.
Frankly, I do believe that automated cars with solve the less than 50 mile commute problems better than light rail. I actually am a little optimistic that one of the hyperloop companies will get it together to create a short elevated line that can actually start a new building phase for rail (well, tube) transport. The danger is that they realize they will probably make more money on cargo and go that way.
1) the compromises on speed are going to make for a lot of controversy if it ever does get done
London to Manchester is somewhat still OK but London to Newcastle takes longer and costs more than London to Brussels via the Eurostar.
The thing that mattered to me is that it was 2 hours, because a 1 hour flight isn't really a 1 hour flight after you deal with the airport.
IIRC the barrier of entry for "High-Speed Rail" in Europe (or in general) is 150-155mph
https://en.wikipedia.org/wiki/High-speed_rail_in_Europe
The UK has only 1 line with a speed permit of upto 300km/h (186mph) which is used for the Eurostar.
It has 4-5 other "fast" lines with a speed limit of 200 km/h (125mph) which doesn't technically count as highspeed.
That said, if you live somewhere with a convenient airport and a decent rental fleet (more places than you'd expect) it's highly liberating. I live near Denver and have gotten bored and flown to Canon city and surrounding areas for the day. Also, Pilots n Paws is awesome
Also, note that minimally you would need a commercial certificate to fly for hire. Even then, there are some restrictions on how you can do that. A private allows you to fly with friends, but you may not charge them. You can share expenses for the flight with friends, but need to be careful that it's legitimate sharing.
Surprisingly economical too, 2000mi on ~$200 in fuel. Probably around $60k to build right now (depending on avionics)
Edit: 100LL (aviation gasoline) is around $4/gal right now, hence the $200 for 52gal