They still need another site between San Diego and LA. Superchargers at either endpoint aren't really useful to me. Maybe those will help offload SJC a little, but not very much, I think, especially with more and more Teslas on the road.
While I agree, there are always those who go to San Diego for the day, or vice-versa, to L.A.. If there is an option to charge at the destination, then one would not need to charge in between. That's exactly what I did on my last trip to SD, though I charged at a hotel overnight. Definitely did not need a charge to get home.