I’m not sure where this idea that subways are fast comes from. The average speed of the NY subway system for example is ~20mph. High speed rail is a different story of course.
You must be talking about Japan or Europe.
The California "bullet train" was / is going to take 4 hours to go SF - LA. Less than driving, but about the same as flying, even when you factor in getting to & from the airports and waiting in the departure lounge.
And of course, the train stations are not "everywhere" either. You have to factor in getting to & from them, too. Especially in LA where you hardly ever want to go downtown.