The 757 and 767 were originally developed as short to medium range aircraft. Then the airlines discovered that the 767 could get certified for extended over-water operations (i.e. Hawaii and trans-Atlantic), and that they could cram more people in smaller aircraft more frequently on the short haul routes. Size doesn't matter, the Japanese were using high capacity 747s on fairly short hauls. What has mattered is if a leg and turnaround is too short; the JT8 powered 737 was a success in Hawaii, however the CFM powered 737 was not as the engines did not have enough time to cool between all the short hops.

Frequent 737 and A32x flights will remain the preferred travel option between northern and southern California, until outside factors push traffic to HSR (regulations, ground crowding around the airports, lack or rental cars, etc). Good thing that Californians are willing to keep throwing unlimited money indefinently at HSR, whether building it or operating it.