The vast majority of local SIA pilots have a very long National Service reserve commitment and can, (and often are), called out at a moments notice. These pilots have to get permission to leave Singapore and as soon as they say why they want to go they are told they will be called up the very day after they have left!!!
Failure to show counts as desertion! The punishments are fierce.
It has nothing to do with courage on their part, the Singapore government has them completely stitched up. The only ones who can move are the Malaysian nationals.
By the time a Singaporean has completed is national Service reserve commitment they are likely to be too old for CAL or senior enough in SIA to make a move uneconomical.