Apparently if you fly Southwest and are trying to get across the country, and something happens and your flight is delayed, you're done for the day. Presuming you're not going from a huge airport.

Today was flying out of SMF, the flight to LAX to connect to New York is delayed, they announce first they'll hold the flight at LA, and then after seeing how much we'll be delayed HQ must've decided it isn't worth it. So no more arriving in NYC on Southwest today.
There was plenty of availability on UA and AA though, and I just paid cash for one of those. But Southwest seems to have no non-stops across the country so from most airports it takes at least two connections to get across. And the fact they don't get you tickets on other carriers means you're pretty much stuck if something happens.