Hawkers have been some of the most habitual gamblers since illegal gambling den days. Good cooking and hawking may be lucrative but it's a tough and dirty job, and many hawkers harboring dreams of easier way to make more money are naturally attracted to gambling. But from then, they developed habit and addiction.
Instead of the initial idea of gambling to win so much money that they could quit their hawking business, it became slogging more on the business to feed their gambling habit. They were ideal customers for illegal gambling dens, bookies and loansharks, since hawking is a daily cash-flow business with lower risk of default.
Now with legalised casinos, the hawkers have a better place to go without worrying about police raids. The better established hawkers are now modern upscaled businesses, some even corporatised. They can qualify for bank and casino credit lines. They're not really cooks and hawkers anymore. They hire other people to do the works. They've become business owners and overseers with lots of money, casual and discretionary time about what they do. The casinos are natural attractions.
As for Ponggol Nasi Lemak, from food quality point of view, I think it has already gone the way of past illuminaries like the once-famous Scissors Cut Curry Rice, Eng Wah Beef Noodle etc. Nothing to shout about compared to common fares from unknown hawkers. But this is Singapore; many Singaporeans have funny sense of taste.