It's mainly to do with lack of aircraft. They are going to have problems from December onwards, with the delay of the A380 and the 744's that have either been sold or are due for maintenance checks.
SQ345/6 has been a cash drain for a while, mainly due to the costs of having to have a crew who board in ZRH, fly to MAN and back to ZRH and have another day off. Nice work if you can get it.
Loads on 345/6 were generally poor ex-MAN, and with the 744 fleet due to be cut further it was only a matter of time.