The SFO PDX nonstop market was permanently discontinued in Nov 2018. After the AS/VX merger it was up to 3x daily at one point, but my guess is that those airplanes were redeployed more profitably elsewhere in the network.

The other consideration at SFO is that the schedule seems to be built to withstand cancellation of a certain number of flights to keep others on time during a GDP. So it also could be that it made more sense to push PNW traffic over OAK and SJC.

SM Disclaimer: These are my own thoughts, not necessarily those of Southwest Airlines.