CA is a third as dense as Japan, as whole.
Tokyo has 8.9M people while LA has 3.9M people; half the number. Osaka (3rd largest) is 2.7M people while San Jose (3rd largest) is just under 1M people; again, half the number. The distance from Tokyo to Osaka is 500km, while from LA to San Jose is 550km. (In both cases, the 2nd largest city is nearby the largest.)
You have half the justification in CA you do in Japan, looking at similar urban areas. In the case of Japan, connecting those two cities goes through another 3 with over 1M population (and totaling over 7M together).
US cities are spread out and relatively low population.