Southwest doesn't go to McAllen Texas (thats a Major International Airport , btw) or Brownsville Texas ... both in the Reo Grande Valley ...
They MAY go to Harlingen, but that just means they are about an hour and a half away, vs 15 minutes.
edit:
Southwest Does go to Harlingen, but like I said, I would have an hour and a half trip to get to the correct city once I get there instead of 15 minutes.
Also, SW makes me go to 2 different airports from Detroit just to get to where I need to go ...
The most lay over I will accept is 1 city.
In this case its either Dallas or Houston for where I go.
Dallas is American and Houston is United.