As said, the TCX model (which has been the main driver to the west coast routes being opened) lends itself to having a few flights a week dotted up the state. Being a leisure airline, this means a passenger could fly into say, SAN, and then depart from LAX, or any number of combinations of SAN/LAX/SFO/LAS. I've done it several times, many others do too.
There is no such rule that a particular route MUST be served at least daily to be able to open up another route. If TCX want to cover their bases by opening up flights to several airports on a less than daily basis (TCX being the carrier rumoured for SAN), then that's what they will do, and it seems to be working for them with SFO added this summer and LAX going to 3 weekly (along with the up to 6 weekly LAS).