Eh, I'm not really buying this is a problem at all. Compared to last year attendance is down slightly. But that will happen, it simply can't keep going up every single year.
Probably almost all of that drop is blameable on the Yankees (bad off season, people expected that team to be weaker than it's been in a while), Boston (coming off a 93 loss season) Miami (FIRESALE!), as well as worse weather than last year. April and May were really unseasonably cool, and already many more rainouts/delays than all of last year.
MLB is in a golden age when it comes to attendance. Look at the numbers for the 1980s and previous.