To everyone saying SF-LA already has plenty of flights, consider the following benefits of trains:
- No need to worry about how much luggage I have. It will likely be a minimal charge if there is even one
- Trains are more comfortable with larger seats, usually
- Trains will make tickets cheaper, putting downward pressure on flight tickets as well (competition)
- Less security theatre and less worrying about what I can and can't carry
- You can still have good internet access
This is in addition to the environmental benefits of trains.
Perfect is the enemy of good. More sections and branches can be added. Piecemeal is how transportation infrastructure grows everywhere. It does not come to fulfill everyone's needs all at once.