Because AS doesn’t have banked hubs, if they don’t have frequent flights in a given market, there are only a handful of connections that are well served from that market. I’ve felt this keenly out of both YLW and EAT (my two home-ish airports). I find that trying to fly AS to anywhere east just doesn’t work. I’m currently on a trip in which it made more sense to drive five hours to GEG and fly GEG-DEN-Wisconsin than to drive one hour to YLW and fly YLW-SEA-MKE because of the infrequency and poor timing of AS options. The YLW-SEA flights are scheduled such that it’s impossible to get to MKE without an overnight or 5+ hour layover in one or both directions.

So yes, in principle they could address this by banking SEA. But I doubt SEA has the gate or runway capacity to handle banking (a la the absurd banking UA has at DEN — practically every city had a flight landing at 15:00 and departing at 15:45, plus or minus ten minutes, something I’m not used to since I rarely fly through a banked hub like DEN) anyway.