The powers that be designed the Sounder platforms in such a way that commuters going to & from their trains do not go through King Street Station. Unless one wants to jump / climb across high - level platforms & cross several depot tracks, you have to go up to the overhead walkways to exit the Sounder platforms. This design works well, as most Sounder commuters exit up & East, across 4th Ave. South to the downtown transit tunnel @ 5th Ave. S.
Amtrak trains use the through track closest to the depot, as well as the stub tracks South of the depot. This works well considering that the morning Cascades trains to Portland & Vancouver B.C. depart during the morning Sounder arrivals.