This is the reason that "they" are scared off. If everyone quits than there goes their millions down the drain.
Actually tobacco duties only accounts for roughly 2% of tax collected(based on 2011 data). It is the lost in revenue from pharmaceutical companies that causes the big hoolabaloo.
Take Sweden for example, Snus has greatly reduced the number of tobacco related diseases(backed by 25 years of clinical data) and as a result people are spending less on health care. This is a disaster for pharma as they can no longer sell as much drugs and services, especially NRT treatments in Sweden. Sweden was a grave disaster for big pharma.
Apply that to Singapore, you get reduced medisave withdrawals, reduce spending on drugs, reduced usage of hospital facilities and expenditure on healthcare greatly reduced. Everything gets dragged down. You think the government would allow this to happen?
Some things are there to force you to spend money.