You didnt say that earlier

Suites are popular as redemption, so iam not surprised that you cant find availabilty in saver. SQs policy to allow credit card point transfers into Krisflyer unfortunately takes its toll on the availabilty of Suites especially on the US-SIN routes.

Either waitlist and book a C redemption as a backup or try to find a route which is less popular if needs to be Suites.