Source: The ABA History: The History of The ABA
The old American Basketball Association is not that different then the old American Football League. The National Basketball Association had around 16-18 clubs, in a country at the time of around 200M people. The National Football League in 1959 had twelve clubs in a country of around 150M people. One of the reasons why the AFL was able to establish itself because there were more cities that wanted pro football clubs than the NFL was willing to respond to. Similar situation as the ABA they knew there were cities ready for major league basketball clubs, that weren't in the NBA. Like Richmond, Lexington, Indianapolis, St. Louis, Houston, San Antonio, Denver, San Diego and others.
And the ABA had the management and financing and believed with the NBA which wasn't a very popular league yet still trailing the NFL and MLB in the late 1960s and early 1970s. That they believed they could attract the management, coaches and players to play in their league by paying their players more and giving them more playing time up front. Because in the NBA some draft picks they were told that they would have a chance to make the team. But the ABA were telling potential draft picks that they would make the team and play. And thats how they lured so many players to the ABA. Players like Julius Erving arguably the best all around player in pro basketball in the 1970s, George Gervin who's in the Hall of Fame, Artis Gilmore, Rick Barry who are also in the Hall of Fame. And many others including head coaches like Larry Brown who's also in the Hall of Fame.
The ABA was also very exciting kinda the way the NBA used to be twenty years ago or so. With a lot of run and gun basketball, fast break teams trapping defenses, the three point shot, the red, white and blue basketball. But one thing that the ABA wasn't able to do was TV. If you weren't going to the games, you probably didn't get to see an ABA game unless you lived in a market with an ABA club and they had local television. Unlike the AFL in the 1960s that had a national broadcast contract with ABC. The ABA wasn't able to get that pro football was more popular than pro basketball at the time.
Football is still more popular that basketball today and had the ABA landed a national broadcast contract like the AFL and even the USFL twenty plus years later, a lot more people would've gotten to see how good of a league the ABA was. Because especially in the early and mid 70s, the ABA playoff teams and champions were just as good as the NBA playoff teams and champions. Teams like the New York Nets, Richmond Squires and Indianapolis Pacer because they had players like Julius Erving, Artis Gilmore, George Gervin and many others.
What the ABA proved was that they were major league basketball and that they were an NBA caliber league if not better. And that they deserved to merge with with the NBA in the late 70s. Teams like the Nets, Pacers, Rockets, Nuggets, Jazz, are all in the NBA right now and for the most part all making money and prospering.