Why would you want to make body armour for all your troops when your not in war status. Body armour doesnt last forever and their is a certain shelf life before it becomes to weak to be used as body armour. China if ever needed can produce them very quickly on their assembly line, around the clock 24/7. PAP deal with criminals that are armed with weapons more then the troops who currently are only training. For those troops sent off to Somalia I've seen footages that have them in full gear, body armour, helmets (not the flimsy ones), tactical radio etc... But I dunno they probably think it looks better in photos to not wear them??
Why wear body armour in training? To get used to the weight and the bulk of the armour that restricts movement. You can do that with other means then wearing body armour.
Doctrine. Do snipers wear body armour, nope. They substitute it with stealth, movement, staminia.