So, am looking into J awards for an Asia trip, but I struggle with the logic. Anyone knows why I am not able to book A-B, but I can book A-B-C?

E.g. I see plenty of ICN-SIN-HKT connections, but not ICN-SIN when checking for that one? Also seeing ICN-FUK-HND-SIN, but if I look for HND-SIN only, it's only showing Y flights and the J connections disappeared.

What's that? Some strange case of married segments for award bookings? Didn't know that's a thing.