Seriously, plenty of other countries have avoided the opioid/fentanyl problem without the death penalty. Doesn’t that imply there’s something different? Perhaps extreme lobbying by opioid manufacturers for doctors to overprescribe them and turning the other way to pill mills? Given the opioid epidemic was driven by legal opioids and the black market grew to supply people who could no longer afford the legal supply, I think that suggests Singapore’s death penalty policy has nothing to do here.
Moreover, I suspect like all places, Singaporians don’t have that much difficulty accessing illicit drugs. Do you think this 1kg represents the totality of the illicit drug trade in Singapore? Heck. If anything the death penalty should be the cause of record profits for black market drug distributors - where there’s more risk you can charge more money because there’s less competition willing to take that risk. That increases prices to a point but it’s not going to price it out of complete reach (otherwise you have no customers).