The other carriers don't get it. You can't just repaint your planes and call it a new product. It's not that easy. Southwest has carved a whole new phenomenon in our flying society.
MetroJet was launched as a single-class, low-frills carrier. However, when they first started, most flights went through their BWI hub. That's just like the United Shuttle flights going through DEN or SFO. Southwest does point-to-point, going to lots of places from lots of places. If one airport gets shut down, Southwest has other options to reroute customers. The others have a harder time.
The other thing is aircraft utilization. An airplane on the ground isn't making money. Southwest keeps their planes on the ground no more than 20-30 minutes. I'd like to see United or US Airways pull that one off for every flight.
Southwest also knows where they SHOULD NOT serve. They avoid congested airports or those that suffer serious delays. Why the heck is MetroJet going into BOS or ATL? That's insane!
A while back, I wrote a post about why I think Southwest is so successful. You'll find it here
If you really want to get a good grasp on how Southwest came into doing so much of what makes them nuts, check out the book Nuts! : Southwest Airlines' Crazy Recipe for Business and Personal Success
. I've set up the search link at Amazon, you'll find it here