This week Delta announced they are launching a shuttle service on the west coast between Los Angeles (LAX) and San Francisco (SFO). But a shuttle between these cities is nothing new, as a matter of fact it's been tried a number of times with the most aggressive being Shuttle by United which operated flights every 15 minutes between the two cities during the 90s on a mix of 737-300s and 737-500s.
However, rather quickly, United learned how bad of an idea it was to run these flights. Rarely were these flights on time, every time I flew these flights we would fly at less than 24,000 feet to minimize flight time (at the expense of fuel burn, but fuel was cheap back then), and coming out of SFO would always mean an extended hold on the tarmac waiting for a slot to take off. Coming out of LAX was worse given the weather fluctuations that SFO experiences, it was a crap shoot. To highlight how bad the operation would back up, it was a fairly regular occurence to see a 747-400 fly this route as much as a few times a day to play catch-up for all the delays and cancelations.
Furthermore, there is a lot of competition from Southwest in this market. For travelers who travel mostly within California, Southwest dominates (I still have yet to understand why). But Delta also faces stiff competition from both United and American and United tends to dominate and protect its west coast markets.
Let's also not forget that Delta abandoned LAX once as a hub and a lot of people who were loyal to Delta back then are still soured by that whole experience and make no secret about it. LAX wasn't the only airport Delta did this to so they have a track record in the department.
Lastly, LAX is a royal pain to deal with. United and Southwest are able to drive a lot of connecting traffic through LAX as they have the feed, Delta doesn't currently use LAX as a big routing hub, so unles that changes, these flights won't be very full. Additionally, United and Southwest both have operations at Orance County, Burbank, and Ontario that feed into SFO, giving travelers a lot more options and the ability to avoid LAX.
In my opinion, I doub this will last for the long haul, but it will be interesting to see how this fairs over time, but it's obvious the Delta Dartboard is running out of space.