I flew AA and UA a lot of out Carlsbad back in the day. They both went to LAX which many times meant an extra stop going East. I then switched when America West started flying to PHX out of CLD because that was a hub.

As someone mentioned earlier. Fog delays are a thing. At LAX United would arrange a bus to drive you to CLD when they could land due to the fog. Personal story: I landed in LAX after a business trip. I walked to the United Express gates and there was a line. I guy walked up behind me and asked, "what's up?" I said fog delay. He asked me if I wanted to split a rental car. I said heck yes. We walked straight to National Car rental, he jumped in a random car and drove me to CLD. I said thanks and handed him $20 and walked to my car. Never saw him again.

I doubt we'll get a bus from SFO or DEN.