If you give users the right self-service options, they'll resolve it for themselves between the start of the outage and when they expected to fly. They'll rebook or take their money and go.
I don't know with Southwest, but I know more than one airline has a system that sends automatic "choose one of these options" emails when flights are cancelled. When all of your customers need new flights, though, the issue isn't how the rescheduling is done, it's the fact that almost nobody is going to be able to choose an option they like.
Anecdotally, it has worked enough times for me to call/talk to an agent vs dealing with the automated suggestion system. Just don't be a jerk.
One automated system gave me a next flight of the following day. Spoke to an agent and was rerouted through another hub and only delayed by two hours overall.
In another case, a delayed flight caused me to miss my connection. Was officially told that I was out of luck and would have to wait (as were the jerks who asked) for the morning. I went and got a seat on the plane out that night.
I wonder if there just isn't a negative feedback loop here (everybody gets helped) so people just assume their way is the most effective.
Those aren't mutually exclusive. You can complain a lot but not be a jerk. You just have to understand and acknowledge the situation the customer service rep is in but still be firm on what you want.