American football is a fascinating game. It has been described by the ignorant and uneducated as just a bunch of fat guys slamming into each other between beer commercials, but what it actually is is a beautiful game combining speed, brute strength, strategy, incredible skill, and resource management.
Resource management? Absolutely. For starters, teams (unlike in soccer) are all constrained to a salary cap, which means that major markets don't always win because they have the most money and therefore can afford all the best players.
Also, because during the year injuries take their toll. Football is a brutal sport with injury a near-constant threat. The Seattle Seahawks faced the Atlanta Falcons two weeks or so ago with their most crucial defensive player out with a broken leg and cornerback Richard Sherman had sufficient injuries to his knee that the league is actually going to penalize the team for fielding a player who was that injured. (The Falcons won handily). Team doctors regularly patch these players up so they can work through inflammation, pain, injury and broken parts, but they're not Dungeons and Dragons style clerics able to cast healing spells. One of the reasons that the New England Patriots do so well is that they have enough depth on the field to compensate for a lost star player. Rob Gronkowski is out with a back injury, but they have a suitable backup.
Also, because of the nature of the draft - the teams that did the poorest get the first pick of incoming players, with the best teams picking last - there's a natural rise and fall to teams, but it also means that you can be drafted into and stay with a terrible team and never realize your full potential as a player. Ask the Falcons' Tony Gonzalez, one of the best players ever to play at his position, but who retired before the team climbed out of mediocrity.
So in theory, the Pro Bowl is an EVENT. What if, just what if, you took the very best players at each position regardless of team and had them play against each other? That would be a REAL draw in the lull between the end of the season and the Super Bowl.
In practice, well....
Firstly - players from the two Super Bowl bound teams don't play. Most often than not that means many of the best players aren't in it.
Secondly - they can't be injured. That takes a significant number of monstrous players out of the pool. Usually teams give their everything in the playoffs,which means people have a higher chance of breakage.
Thirdly - what exactly does this game DO for a player? Not much. It doesn't advance their team, nobody really cares about the game so it doesn't advance their personal brand, and if they get injured in the game there goes that next season's contract or in the case of a free agent - their entire marketability. If a really talented player is coming available by league rules, the last thing they want to get before summer negotiations start is any kind of injury.
So in essence, it's a few great players and a lot of good ones doing a meaningless scrimmage in Florida.
Nobody watches it, nobody involved in it sees it as any more than a consolation prize, and the score is just for bragging points.