Or the 5th carrier on LAX-SEA which currently has 32 daily flights:
AS 15x daily
DL 10x daily
AA 5x daily
UA 2x daily
AS, DL, AA, UA, and WN all currently serve SLC nonstop from LAX, and there is significantly more O&D demand on SEA-LAX than there is on SLC-LAX.
AS, DL, AA, UA, WN, and NK all also serve Dallas nonstop from LAX, but WN and AS serve only DAL in the DFW Metroplex nonstop from LAX whereas AA, DL, UA, and NK serve only DFW in the DFW Metroplex nonstop from LAX.
Here is the breakdown of the number of nonstops on LAX-SLC: DL (8x), AA (4x), WN (3x), UA (2x), AS (1x)
Here is the breakdown of the number of nonstops on LAX-DFW/DAL: AA (13x to DFW), DL (4x to DFW), UA (3x to DFW), NK (3x to DFW), WN (4x to DAL), AS (3x to DAL)
There is room for WN to add LAX-SEA nonstop service with VX no longer around and with NK no longer serving SEA nonstop from LAX. If Dallas and Salt Lake City can support nonstop service out of LAX on AS, DL, AA, UA, and WN, SEA can probably support nonstop service to LAX on WN in addition to AS, DL, AA, and UA. The O&D demand is also greater on LAX-SEA than on LAX-Dallas or LAX-SLC.
In Q3 2017, the average number of passengers per day on LAX-SEA was 5,576 passengers a day (both directions), compared to 4,534 passengers a day on LAX-DFW/DAL and 1,718 passengers a day on LAX-SLC.