Good article explaining why Singaporeans don't smile. This was written almost 10 years ago! Nothing has changed since. This is also the reason why we didn't salute officers in Mindef. There's just too many of them!!

From yawningbread.org
Since before humans evolved from monkeys, such agonies have afflicted every individual. Love-struck and dumb-struck. Unless I am qualified to discuss hormonal physiology, nothing much I can say about that.
I just wonder sometimes whether Singaporeans have a little harder time of it, because we are generally conditioned to be less than sociable. At moments when we want to meet people, we find we don't have the skills to make conversation. We're just tongue-tied and frozen.
Some people will say it's our Chinese or Asian culture. I don't really buy it. I believe there is so much variability in Asian cultures, that it is over-simplistic. There may be some truth in it, but not enough to explain it all.
To me the more obvious reason why Singaporeans find it hard to be convivial is that we are urban creatures. Urban denizens adopt a code of behaviour in public which aims to keep social interactions to a manageable minimum. We see, literally, thousands of other people a day. We are jampacked into lifts, buses and trains. Lunchtime finds us in a crowded foodcourt, sharing a table with 2 other strangers. We can't afford to greet them all.
How about a smile and a nod at least, as a simple act of courtesy to those around? Singaporeans don't even do that, and I can understand at least one reason why we don't. Out of the thousands of people we come within eyeshot of every day, the probability is that at least one or two will be mad. Insane. Mental. You smile unknowingly at one, and you don't know what the consequences will be. Self preservation alone says "don't smile at strangers."
So the rational thing to do is to have this common practice whereby everybody ignores everybody else. You don't impose on me and I don't impose on you. We stand quietly and look blankly at the floor counter as the lift goes up, or daydream through the window as the bus trundles along. Don't look people in the eye unless you actually know the person. Don't start talking to strangers for no compelling reason.
Our urban customs are really social graces. They make it easy to live together in a crowded environment. We compensate for the lack of physical space and privacy by creating mental privacy, and we've learnt to do that almost instinctively.
The problem with instincts is that when circumstances call for the opposite, we may not be able to overcome them and do as our head or heart desires. We can't find the words to offer a greeting let alone open a conversation; we can't even raise our face muscles into a smile. We are conditioned to fear that we'd be committing a serious breach of urban etiquette, and that we'd be shunned and rebuked with a "is this guy mental?" stare, all this in full public view. Not forgetting too, that we all fear rejection and having our heart and hopes fracture into ten thousand pieces all over the pavement, for the rest of humanity to walk over.
Yes, but can I offer any advice? Alas, no. I am human myself, and I suffer through it all too. But I thought I'd write about it anyway, to let you know, you're not alone.
© Yawning Bread