As a frequent flyer- I pack light and use the overheads. Yeah, I’m guilty of jockeying for position. I’m lifetime Silver on DL and hoping for annual Silver this year on CO. I still love WN and fly them when it fits. Sometimes they are the least expensive, sometimes not. I do think ala carte is a pain in the butt, however I understand internet pricing is driving it. Everybody "homes in" on that first published number. That said, I have my preferences and needs when I book my flights, in rough order-

Price- driven by my business cost
Schedule - driven by what I need to do
Seating- I'm not sitting in a middle seat for 4-5 hours if I don't have to- driven by comfort
Preferred Carrier- based on ease of use (primarily boarding preference to get overhead space) driven by what I want or expect for convenience or service
Frequent Flyer Benefits - driven by what I might accrue long term

The bags are kind of a non-issue. How does WN win? Fun airline to fly on, excellent in-flight service, and perhaps most importantly, they are not trying to be low bidder on Orbitz, Travelocity, etc.