Although gambling has always been an important part of Atlantic City's economy, it's not until its legalization in 1976 that we see how powerful the industry has become.
Fed up with their decline from "a prosperous and bustling seaside resort" to "a sleazy saltwater ghetto" (9.4), Atlantic City residents pour their hopes into legalized gambling. After all, widespread (illegal) gambling was Atlantic City's most effective tool for drawing in tourists until the local political machine collapsed, bringing racketeers and gambling houses down with it. So maybe legalizing it will help bring the tourists back.
Legalized gambling represents a new approach to an old system. Instead of placing the reigns in the hands of political bigwigs or conniving Mafiosos, the people want to see respectable businessmen running the show. Of course they might have reconsidered if they realized that their "respectable businessman" would turn out to be Donald Trump, but hey—you win some, you lose some.
Ultimately, the rise of legalized gambling reflects growing changes within Atlantic City and America as a whole. Gone are the days when local political parties and criminals run the show—"criminal types […] never had a prayer of dominating Atlantic City as they had" (11.51) before. Atlantic City is now corporate turf and only time will tell if this is a change for the better.