No one is really talking about connecting tiny places really faraway from each other. But cities in 1-6 hours drive of each other and sensible locations inside them clearly make very much sense to connect with public transit.
Unless almost everyone who wants to travel already owns a car which they and their family can quickly, safely and directly drive (with reasonable luggage) to the very doorstep of any given 1-6 hour destination. Which is the case in the US. Will be even more the case if cheap Chinese electric cars ever hit the shores. Makes very much less sense then.
San Francisco to LA is about a seven hour drive. It’s about 90 minutes flight, plus getting to the airport and getting through security in the airport and all the general airport-induced slowness. Given a top-quality conventional high-speed line (300km/h) it would be two hours (so in practice faster than the flight).