Can someone explain to me why his strange quirk is happening. I'm going to phone BA and enquire about it but thought someone on here might be able to explain it first

I'm looking for reward seats to Singapore or Kuala Lumpur on BA. If I search to SIN it comes up with a BA flight to KL then a Malaysian flight for the other leg, now trying to use my 241 so this isn't an option for me

However if I search reward flights to KUL I cannot see those flights. Why would there be reward availability enroute to SIN but not direct to KUL? Are there separate award buckets?