Much as I respect @LSLGuy as one of the most helpful and informative posters on SDMB, I need to take exception with this statement, not because it isn’t at least partly true, but because it doesn’t tell the whole story.
I agree that Southwest’s fares aren’t as low, relative to other carriers, as they once were. But one of the primary reasons I fly with Southwest whenever I possibly can is that when I look at fares on Southwest’s website, I know that’s the price I’m actually going to pay. Whereas the base price given by virtually every other airline is almost certainly not.
The price of every ticket on Southwest includes:
2 free checked bags
1 free carry-on and personal item
Your choice of seat (because of their open seating policy)
And, as I mentioned above, they don’t charge extra you to change or cancel your flight.
Most other airlines show you a price that does not include any checked bags, and many will charge you for a carry-on, and to select your seat in advance, which means that if you do not pay the extra fee, you might not be able to sit next to your traveling companion. So that low fare might end up costing you $100+ more per seat when you add the fees. It’s bait-and-switch.
Also, I prefer Southwest’s open seating procedure, because it’s much faster to board than the other airlines’ methods. If you book far enough ahead to get into Southwest’s A boarding group, you will pretty much have your choice of any seat, including the emergency exit rows. And yes, you can pay extra to get Early Bird or Priority seating.
I don’t know why Southwest doesn’t allow their seats to be sold through other providers (ISTR hearing that they are still using a really old computer system that doesn’t allow it), but I wouldn’t be surprised to learn that it’s because their fares, which include all the extras, wouldn’t look good compared to other airlines, which don’t.
Of course, if you want or need first, business, or premium economy, Southwest is not the airline for you.