This project is already grade-separated in the sense that there are no level crossings: even though they're in the "empty" central valley, there's still hundred

This project is already grade-separated in the sense that there are no level crossings: even though they're in the "empty" central valley, there's still hundreds of grade-separated crossings that need to be built, not just through the cities, but also rural roads as well. So while it's cheaper out in the Valley than in LA or SF, it's still significantly more expensive than a non-grade-separated, say, ~75-100 mph-rated track would entail, the sorts of which are common in Europe and do a decent job moving people around cities spaced at such distances.