But American went for CVG-PHX instead... a market that is now so oversatured its unreal. No midsize airport needs 3 LCCs (Southwest, Frontier and Allegiant [AZA] ) and 2 legacy carriers (Delta and American) serving a single airport with limited demand — especially Phoenix. One or two is bound to fail.
United should certainly re-enter this market from Cleveland. They already have a following here, why not take advantage of a route starved for legacy service?
WN will also be reducing BUF-PHX and SDF-PHX nonstop service to weekend-only starting on January 4, 2020.
BNA and TUL are also the only remaining destinations with year-round, daily nonstop service to PHX on WN but not on AA.
WN was also able to make daily CVG-PHX seasonal nonstop service work in both Spring 2018 and Spring 2019 as WN had load factors of over 88% on CVG-PHX in both Spring 2018 and Spring 2019. There is also likely enough demand for more than just F9 on CVG-PHX on a year-round basis as the PDEW on CVG-PHX (excluding G4 CVG-AZA) was 183 passengers/per day in 2018.
WN can likely make CVG-PHX nonstop service work on a year-round basis as WN would have connecting feed from Southern California and O&D from Greater Phoenix to support CVG-PHX nonstop service, whereas F9 and G4 have to rely on more O&D on both ends of the route to make CVG-PHX/AZA nonstop service work. WN also has 737-700's with fewer seats than F9's A320's or G4's A319's that can be used on the CVG-PHX nonstop route.
MCI and STL are both mid-sized Midwestern airports that have 5 or more daily nonstops to PHX, but WN has a much bigger presence at MCI and STL than at CVG, CMH, or CLE. There are also fewer carriers serving the PHX/AZA market nonstop from MCI and STL than from CVG.
Even though WN decided to reduce CLE-PHX nonstop service to weekend-only starting on January 4th, there was likely enough demand for WN to operate daily CLE-PHX nonstop service on a year-round basis as the load factors on CLE-PHX was over 90% in 2018 and over 88% in the first 4 months of 2019.
AA and WN both have a stronger FF base in the Greater Phoenix market than UA does, and there are also some WN FF's in Greater Phoenix who prefer to fly on WN over AA or UA due to WN having nonstop service out of PHX to destinations that AA or UA don't serve nonstop from PHX.