Because it's easier to digest in such a compact package. Violence and Saturday-Sunday has been a football tradition in this country since I was a little kid.
In the NFL this very season they were already talking about Bills-Jets in Week 2 and that the loser is almost certain to miss the playoffs...2 games in.
The NBA suffers from these extremely long seasons that really doesn't mean much of anything until after the all-star break. On top of that, in the NBA if you have LeBron James or some other world type of talent on your team it is almost a guarantee that you will be one of the final 4 teams left. LeBron has made 6 straight NBA Finals...think about that for a second. In the NFL the Quarterback is the most important position, but Brady/Manning and the other elite Quarterbacks have absolutely no shot of ever going to 6 straight Superbowls. The Bills went 4 straight times a long time ago due to a terrible conference, but that will likely NEVER happen again.
You can have the best pitcher or hitter in baseball...doesn't even guarantee you a spot in the playoffs.
You can have the best QB in football and that doesn't guarantee you a spot in the playoffs.
You have a top 2-3 talent in the NBA? Yeah there is a good chance you are going to the playoffs with a damn good shot at going to at least the conference finals.
Basketball is still my favorite sport though. I do think that the NBA is in the best position to ever take over as the #1 sport in this country if the health issues continue to be a strong topic in the mainstream, but that will likely not happen in 20-30 years from now...when most of us on here will either be retired or not care as much.