Alaska Airlines partners with Singapore Airlines. Alaska has access to more award space than other Singapore Airlines partners. Usually partner airlines, like fellow Star Alliance members United and Avianca, cannot book business or first class long haul awards on Singapore Airlines at all.
Alaska not only is able to book premium cabin awards between the U.S. and Asia on Singapore Airlines but Alaska seems to show availability soemtimes when Singapore isn’t offering the space to its own Krisflyer members.