There may be some "factors", but, sorry, no excuses. Alaskan pilots are not unfamiliar with SEA. We count on professional pilots to perform professionally. But for the grace of God there was no one else on the taxiway when they landed. This could have been a much different thread.
I hope that every opportunity is taken at Alaska and other airlines as well to emphasize proper practices with their pilots.
There is some good news in that Honeywell has introduced Smart Landing which should "advise" pilots when they line up not on a runway.