the most expensive option. I think that at this point I've only flown them twice in the last 10-15 years, even though I check them almost every time I travel domestically.

Today, a flight that is $267 roundtrip on Delta or Alaska, is $401 on Southwest, and this is the cheapest option, requiring a 6 am departure on one of the legs. This is pretty typical of what I usually find when I check them; and often the price gap is much larger.

The only thing I can think of is that maybe their tickets are more reasonable if you buy them way in advance, like 6 months ahead. And maybe there are a few cities where they have a hub and offer more reasonable pricing (maybe Phoenix)?