Seems that the OOL-SIN services didn't meet break-even limits and/or yields for Scoot to continue services after the Queensland Government's AAIF taxpayer subsidy period.
https://www.singaporeair.com/saar5/pdf/Investor-Relations/Financial-Results/SGXNET/bu-q3fy2223.pdf (Page 5)
https://www.singaporeair.com/saar5/pdf/Investor-Relations/Financial-Results/SGXNET/bu-q3fy2223.pdf (Page 5)