The SF-LA transit project isn't a replacement for driving, it's a replacement for flying. Cars are replaced by local transit, the CA high speed rail line goes through a whole lot of nothing (read: the worst farmland they could route through) between SF and LA. Are you sure you live around here if you're this off-base with the basic premise?
People have a habit of arguing online that this would replace people's commutes.
Which, to be fair, people online have a habit of just arguing past each other.
This is completely the wrong way of thinking about it. Long distance and short distance transport form a symbiotic relationship.
And in most countries we wouldn't call multiple cities of 100k+ population 'nothing'.
HSR is the spine of the transportation network, that local and regional traffic docks to making a greater whole. It increases the reach and power of public transport as a whole.
For HSR to be successful, you need people using the in-between station for regional trips, not just end to end airplane like trips.