You know, Bud Selig goes around saying 'baseball's more popular than ever', and on the face of it it sounds exactly like what the commissioner of the league would be required to say, but there's actually a fair amount of evidence that he's right.
Not sure about that. When I hear that Pats pre-season games get higher ratings than Red Sox regular season games in August, that tells me that interest in baseball is at an all-time low.
More people watched the NFL draft than the NBA playoffs, does that mean that interest in the NBA is at an all time low?
The Red Sox are in the middle of a miserable season, and the NFL stomps all over everything in the ratings all the time anyway. The NFL is certainly more popular than any other sport in America, but that has no bearing on what we're talking about.
It's more accurate to say that
every sport in America is experiencing an uptick in popularity. Sure, more people might watch football than baseball, but that shouldn't infer that baseball is on the decline because of it.
Here's a good Forbes article that shines a light on how the MLB's revenue has changed (which is a strong indicator of fandom and interest, since you don't get these sorts of broadcast deals if no one's watching)
http://www.forbes.com/sites/maurybrown/2014/01/07/mlbs-billion-dollar-tv-deals-free-agency-and-why-robinson-canos-deal-with-the-mariners-isnt-crazy/