Contrary to what many others apparently believe, I do not think that pool's relative unpopularity is due to a bad image. Look at the most popular sports in this country; football, baseball, basketball, NASCAR, maybe boxing (not as popular as it once was, but can still command big bucks for premium fights).
Baseball is tainted by steroid use. Basketball has had brawls in recent years, and now has a referee scandal on its hands. NASCAR drivers are constantly getting into battles on and off the track, accusing one another of cheating, while cars are also failing inspections. Football has Michael Vick, Pacman Jones, Tank Johnson, Ricky Williams and all kinds of shady characters, and is still far and away the most popular sport in America. And what can we say about boxing? It has been tarnished by scandals its entire history, with also the occasional biting of an ear.
While these issues have dampened the enthusiasm among some fans and undermined the popularity of these sports to some degree, they are still huge money makers and still far and away the most popular sports in this country.
The sad fact of the matter is, I am afraid to say, that in today's society and culture, the sport of pocket billiards simply does not appeal to the tastes of the majority of American sports fans. It's too subtle, and frankly too mysterious for most of them to understand or appreciate, and it doesn't have the action and frenzy and excitement, for the majority of sports fans, that the big-time sports have.
The days in which a sport that is as cerebral, subtle, and beautiful, as pool is can appeal to the masses are long gone. That is why there is no huge fan base in pool, and that is why there is no money in pool (at least in the U.S.).